WE CLAIM:
1. An aging degradation diagnosis apparatus comprising:
a degradation pattern generation unit for generating, from phase signals obtained at a plurality of times, the phase signals indicating a phase of an alternating voltage applied to an apparatus to be diagnosed, and from measured signals measured at a plurality of times by a sensor that is measuring a degradation state of the apparatus, a degradation pattern indicating a distribution of signal intensities of the measured signals and the phase of the alternating voltage;
a histogram calculation unit for calculating a gradient vector of a signal density at each of distribution points of the degradation pattern generated by the degradation pattern generation unit, and calculating, for each of phase ranges different from each other, from the calculated gradient vector, a histogram in a gradient direction of the signal density within the relevant phase range;
a feature vector generation unit for generating a feature vector in which bin values of the histogram for each of the phase ranges calculated by the histogram calculation unit are lined up; and
a degradation cause identification unit for searching for, from among feature vectors by degradation cause, a feature vector similar to the feature vector generated by the feature vector generation unit, and identifying a degradation cause of the apparatus.
2. The aging degradation diagnosis apparatus according to claim 1, wherein
the degradation pattern generation unit divides a plane in which a first axis
thereof is a phase of an alternating voltage, and a second axis thereof is a signal intensity of a measured signal, into a plurality of blocks, and generates, as the degradation pattern, a pattern indicating the number of sets of the phase signal and the

measured signal that belong to each divided block.
3. The aging degradation diagnosis apparatus according to claim 2, wherein
from the number of sets of the phase signal and the measured signal that belong
to each block, indicated by the degradation pattern generated by the degradation pattern generation unit, the histogram calculation unit calculates a gradient vector of a signal density at a distribution point of each block.
4. The aging degradation diagnosis apparatus according to claim 1, comprising:
a feature vector storage unit for storing feature vectors in which a degradation
cause is known;
a representative vector calculation unit for collecting a plurality of feature vectors the same in degradation cause as each other, from among the feature vectors stored in the feature vector storage unit, and calculating a representative vector of the degradation cause from the collected feature vectors; and
a representative vector storage unit for storing, as the feature vector by degradation cause, the representative vector calculated by the representative vector calculation unit.
5. The aging degradation diagnosis apparatus according to claim 1, wherein
the degradation cause identification unit calculates similarities between the
feature vectors by degradation cause and the feature vector generated by the feature vector generation unit, compares the calculated similarities, and from among the feature vectors by degradation cause, searches for a feature vector similar to the feature vector generated by the feature vector generation unit.

6. The aging degradation diagnosis apparatus according to claim 1, comprising
a degradation determination unit for determining, from the measured signals of the sensor that is measuring the degradation state of the apparatus, whether or not degradation is occurring in the apparatus, and only in a case where it is determined that degradation is occurring, outputting the measured signal, and a phase signal obtained at a same measurement time as a measurement time of the measured signal, to the degradation pattern generation unit.
7. An aging degradation diagnosis method comprising:
from phase signals obtained at a plurality of times, the phase signals indicating a phase of an alternating voltage applied to an apparatus to be diagnosed, and from measured signals measured at a plurality of times by a sensor that is measuring a degradation state of the apparatus, generating, by a degradation pattern generation unit, a degradation pattern indicating a distribution of signal intensities of the measured signals and the phase of the alternating voltage;
calculating, by a histogram calculation unit, a gradient vector of a signal density at each of distribution points of the degradation pattern generated by the degradation pattern generation unit, and for each of phase ranges different from each other, calculating, from the calculated gradient vector, a histogram in a gradient direction of the signal densities within the phase range;
generating, by a feature vector generation unit, a feature vector in which bin values of the histogram for each of the phase ranges calculated by the histogram calculation unit are lined up; and
searching for, by a degradation cause identification unit, from among feature

vectors by degradation cause, a feature vector similar to the feature vector generated by the feature vector generation unit, and identifying a degradation cause of the apparatus.