An insulation deterioration determination method executed by a computer device including a CPU that is adapted to determine a degree of insulation deterioration occurring in a power transmission cable and a storage device , the method comprising: a first step of sequentially generating a plurality of distribution patterns (T' 1 , ..., T' 16 ) by standardizing a distribution pattern (T) of a combination of charge amounts and phase angles of each one of a plurality of insulation deterioration pulses (PL) occurring in a period corresponding to several applied voltage cycles of an applied voltage signal (SG2), a second step of executing a first classification process in which the plurality of distribution patterns (T' 1 ,..., T' 16 ) is classified into at least one class on the basis of a standard distribution pattern for each class, wherein each class is adapted to indicate a deterioration stage, wherein each class is determined by comparing the plurality of distribution patterns (T' 1 ,..., T' 16 ) with the standard distribution pattern which is created in advance and stored in the storage device , and wherein a second classification process is executed, in which the plurality of the distribution patterns (T' 1 , ..., T' 16 ) is classified so that the distribution patterns (T' 1 , ..., T' 16 ) are grouped into at least one cluster (A1, A2) by using an algorithm such as a principal component analysis method or k-means clustering; a third step of evaluating a classification result by the first classification process on the basis of a classification result by the second classification process; and a fourth step of determining the degree of progress of the insulation deterioration occurring in the power transmission cable on the basis of an evaluation result in the third step. a first step of sequentially generating a plurality of distribution patterns (T' 1 , ..., T' 16 ) by standardizing a distribution pattern (T) of a combination of charge amounts and phase angles of each one of a plurality of insulation deterioration pulses (PL) occurring in a period corresponding to several applied voltage cycles of an applied voltage signal (SG2), a second step of executing a first classification process in which the plurality of distribution patterns (T' 1 ,..., T' 16 ) is classified into at least one class on the basis of a standard distribution pattern for each class, wherein each class is adapted to indicate a deterioration stage, wherein each class is determined by comparing the plurality of distribution patterns (T' 1 ,..., T' 16 ) with the standard distribution pattern which is created in advance and stored in the storage device , and wherein a second classification process is executed, in which the plurality of the distribution patterns (T' 1 , ..., T' 16 ) is classified so that the distribution patterns (T' 1 , ..., T' 16 ) are grouped into at least one cluster (A1, A2) by using an algorithm such as a principal component analysis method or k-means clustering; a third step of evaluating a classification result by the first classification process on the basis of a classification result by the second classification process; and a fourth step of determining the degree of progress of the insulation deterioration occurring in the power transmission cable on the basis of an evaluation result in the third step. <EOS>