What is claimed is:
1. A combine harvester comprising:
a thresher for threshing grain culms reaped from a field;
a conveyance mechanism for conveying grains obtained by the thresher to a grain tank;
a measurer for measuring an amount of grain conveyed to the grain tank as a conveyed yield;
a yield assignment calculator for calculating a minimal section yield, which is a yield per minimal section, by assigning the conveyed yield to a minimal section of the field;
a grain conveyance state detector for detecting a grain conveyance state of the conveyance mechanism;
a yield corrector for correcting the minimal section yield in accordance with the grain conveyance state; and
a yield distribution data generator for generating yield distribution data representing a yield distribution in the field, based on the minimal section yield.
2. The combine harvester according to claim 1, wherein
the grain conveyance state detector detects a drop in a conveyance speed of the conveyance mechanism and restoration from the drop in the conveyance speed, and
the yield corrector corrects a decrease in the minimal section yield due to the drop in the conveyance speed and an increase in the minimal section yield due to the restoration from the drop in the conveyance speed.
3. The combine harvester according to claim 2, wherein
the yield corrector corrects the decrease in the minimal section yield and the increase in the minimal section yield, using an average minimal section yield obtained by averaging the decreased minimal section yield and the increased minimal section yield.
4. The combine harvester according to any one of claims 1 to 3, wherein
the yield assignment calculator has a delay correction function of correcting a delay time occurring between a grain culm reaping position and the measurer, and a

position shift correction function of correcting a position shift between the grain culm reaping position and a vehicle position measuring point obtained through satellite navigation.
5. The combine harvester according to any one of claims 1 to 4, wherein
the measurer calculates the conveyed yield per unit of travel, based on an accumulation time required to accumulate a predetermined volume of grain, and a vehicle speed.
6. The combine harvester according to claim 5, further comprising:
a yield measurement container for temporarily accumulating at least some of the grains supplied to the grain tank,
wherein the measurer measures the accumulation time using the yield measurement container.
7. A combine harvester comprising:
a reaper for reaping grain culms from a field;
a thresher for threshing the grain culms reaped by the reaper;
a grain tank for storing grains obtained through the threshing of the thresher;
a measurer for measuring, as a unit yield, an amount of grain conveyed to the grain tank while traveling a predetermined travel distance;
a yield assignment calculator for calculating a minimal section yield, which is a yield per minimal section, by assigning the unit yield to a minimal section of the field;
a reaping checker for outputting a check signal at detection of a start and an end of the reaping of grain culms by the reaper; and
a unit yield corrector for correcting the unit yield at the start and the end of the reaping in response to output of the check signal.
8. The combine harvester according to claim 7, wherein
the reaping checker outputs a first check signal at detection of the start of the reaping of grain culms by the reaper, and outputs a second check signal at detection of the end of the reaping of grain culms by the reaper, and
the unit yield corrector uses, as a reaping-start unit yield, which is a unit yield of grain culms that are reaped immediately after the first check signal is output, a unit

yield that is obtained subsequently to the reaping-start unit yield, and uses, as a reaping-end unit yield, which is a unit yield of grain culms that are reaped immediately before the second check signal is output, a unit yield that is obtained before the reaping-end yield.
9. The combine harvester according to claim 7 or 8, wherein
the yield assignment calculator has a position shift correction function of correcting a position shift between the grain culm reaping position and a vehicle position measuring point obtained through satellite navigation.
10. The combine harvester according to any one of claims 7 to 9, wherein
the measurer calculates the unit yield based on an accumulation time required for a predetermined volume of grain to accumulate, and a vehicle speed.
11. The combine harvester according to claim 10, wherein
a yield measurement container for temporarily accumulating at least some of the grains supplied to the grain tank is provided, and the measurer measures the yield based on a grain accumulation state in the yield measurement container.
12. A combine harvester comprising:
a threshing apparatus;
a grain tank arranged adjacent to the threshing apparatus; and
a grain-lifting apparatus for conveying grains collected by the threshing apparatus to the grain tank,
wherein the grain-lifting apparatus comprises a vertical conveyor extending upward from a lower portion of the threshing apparatus, and a horizontal conveyor for discharging grains from a discharge port formed at a leading end portion thereof into the grain tank, the horizontal conveyor extending horizontally from an upper end portion of the vertical conveyor and inserted into an upper portion, on one side in a front-rear direction, of a side wall of the grain tank,
the horizontal conveyor includes a screw portion on a base end side close to the vertical conveyance portion, and a blade portion that rotates to throw grains from the discharge port toward the other side in the front-rear direction in the grain tank, the blade portion being supported by a rotary shaft extending from a screw shaft of the screw portion and protruding in a radially outward direction from the rotary shaft on a

leading end side distant from the vertical conveyor, and
a throwing face of the blade portion tilts toward the side wall side.
13. The combine harvester according to claim 12, wherein
a peripheral portion of the rotary shaft is provided with a stay portion for attachably and detachably supporting the blade portion, and
the stay portion is located on a side opposite to the throwing face relative to the blade portion.
14. The combine harvester according to claim 13, wherein
an angle adjuster for changing a tilt angle of the throwing face is provided so as to span the blade portion and the stay portion.
15. The combine harvester according to any one of claims 12 to 14, wherein
an opening portion from which the grains can be taken out downward is provided in an intermediate portion, in a longitudinal direction, of a casing of the horizontal conveyor, and
a sensor for temporarily receiving the grains taken out from the casing and detecting a grain state is provided below the opening portion within the grain tank.
16. The combine harvester according to any one of claims 12 to 15, wherein
an outer diameter size of a leading end-side casing portion of a casing of the horizontal conveyor, the leading end-side casing portion being on the blade portion side, is larger than an outer diameter size of a base end-side casing portion of the casing, the base end-side casing portion being on the screw portion side, and an outer diameter size of the blade portion is larger than an outer diameter size of the screw portion,
a chamfered portion is formed at a corner of a peripheral portion of the blade portion on the screw portion side, and
a leading end portion of the base end-side casing portion extends up into the leading end-side casing portion on the base end side, and an inner diameter portion side of the blade portion relative to the chamfered portion is inserted in the leading end portion of the base end-side casing portion.
17. The combine harvester according to any one of claims 12 to 16, wherein

the horizontal conveyor is inserted in an upper front portion of the side wall of