We Claim:
1. A mobile communication device to be mounted on a mobile object and perform radio communication with a ground base station, the mobile communication device comprising:
a radio wave condition monitoring unit capable of monitoring radio wave conditions of a plurality of communication media to be used for communication with the ground base station;
a storage unit to store communication medium information, the communication medium information indicating a communication medium having a good radio wave condition in each of a plurality of travel sections into which a route is divided, the mobile object traveling on the route;
a switching control unit to perform control for switching a communication medium to be used, on the basis of the communication medium information when the travel section in which the mobile object is traveling is changed; and
a radio communication switching unit to switch the communication medium to be used, under control of the switching control unit, wherein
when the mobile object moves from a first travel section to a second travel section, the switching control unit causes the radio wave condition monitoring unit to monitor, in a monitoring area, a radio wave condition of a first communication medium and a radio wave condition of a second communication medium, the first communication medium having a good radio wave condition in the first travel section, the second communication medium having a good radio wave condition in the second travel section, the monitoring area being a preset area including a boundary between the first travel section and the second travel

section, the switching control unit instructing the radio communication switching unit to perform switchover from the first communication medium to the second communication medium, on the basis of monitoring results provided by the radio wave condition monitoring unit.
2. The mobile communication device according to claim 1,
wherein
the switching control unit controls the radio wave condition monitoring unit not to monitor the radio wave conditions of the communication media outside the monitoring area.
3. The mobile communication device according to claim 1
or 2, wherein
to collect information on the radio wave conditions of the communication media to be used for generation of the communication medium information, the switching control unit controls the radio wave condition monitoring unit to monitor the radio wave conditions of the communication media on the route, and stores the information on the radio wave conditions of the communication media into the storage unit.
4. The mobile communication device according to claim 3,
wherein
when an instruction position being a position on the route at which the switching control unit has instructed the radio communication switching unit to perform switchover from the first communication medium to the second communication medium is different from the boundary, the switching control unit stores information on a difference between the instruction position on the route

and the boundary into the storage unit.
5. The mobile communication device according to claim 4,
wherein
the switching control unit changes a size of the monitoring area on the basis of the information on the difference.
6. A communication medium information generating device
comprising:
an acquisition unit to acquire the information on the radio wave conditions of the plurality of communication media collected by the mobile communication device according to claim 4; and
a generation unit to generate communication medium information by using the information on the radio wave conditions of the plurality of communication media acquired by the acquisition unit.
7. The communication medium information generating device
according to claim 6, wherein
the acquisition unit acquires the information on the difference from the mobile communication device, and
the generation unit modifies the communication medium information by using the information on the difference.
8. A communication medium switching method in a mobile
communication device to be mounted on a mobile object and
perform radio communication with a ground base station, the
communication medium switching method comprising:
when the mobile communication device stores communication medium information, the communication medium information being information indicating a communication

medium having a good radio wave condition in each of a plurality of travel sections into which a route is divided, the mobile object traveling on the route,
when the mobile object moves from a first travel section to a second travel section, a monitoring step of monitoring, by a radio wave condition monitoring unit, a radio wave condition of a first communication medium and a radio wave condition of a second communication medium in a monitoring area, the first communication medium having a good radio wave condition in the first travel section, the second communication medium having a good radio wave condition in the second travel section, the monitoring area being a preset area including a boundary between the first travel section and the second travel section; and
a switching control step of controlling, by a switching control unit, switchover from the first communication medium to the second communication medium on the basis of monitoring results in the monitoring step.