1. A partial discharge measurement method, comprising: simultaneously measuring electromagnetic waves generated in a sample by a plurality of electromagnetic sensors; separating partial discharge from noise by comparing spatial intensity distribution of the measured electromagnetic waves with preliminarily-measured signal spatial intensity distribution at the time of occurrence of partial discharge, detecting a defect position using a peak position of the separated partial discharge signal; measuring a discharge amount signal by an apparent charge of partial discharge detector along with the electromagnetic signal measurement; and assessing a risk of partial discharge defect at the defect position based on the discharge amount signal.