According to the present invention, after a predetermined voltage is applied to a coil in a state in which the inside of an electric compressor is filled with dielectric liquid and the coil of a motor is immersed in the dielectric liquid, in a first test process, a test product in which a current value when a first predetermined time T1 elapses I1 is less than or equal to a first reference current value is determined as an acceptable product, in a second test process, among the test products in which the current value is greater than the first reference current value in the first test process, a test product in which a current value I2 when a second predetermined time T2 longer than the first predetermined time elapses is less than or equal to a second reference current value is determined as an acceptable product, a test product in which the current value is greater than the second reference current value is determined as a disqualified product, and the first reference current value is a predictive reference current value that allows a test product which is to be determined as a disqualified product in the second test process to be determined as a disqualified product in the first test process, and allows some test products which are to be determined as an acceptable product in the second test process to be determined as a disqualified product in the first test process.