To provide a method for optimizing an inclination defining voltage value of a voltage wave-form allowing an optimum value to be found for expressing the inclination of the voltage wave-form.

This method is provided with a first process for finding a plurality of voltage wave-forms having a time constant of a load model adjusted so as to equalize delay time Td in a target cell 13 by using a circuit for impressing the target cell 13 with a voltage wave-form 10 changing from one level to the other via the load model from a drive cell, a second process for finding an inclination defined as time difference for crossing two or more voltage values relative to a power supply voltage on each of a plurality of voltage wave-forms found in the first process, and a third process for finding two or more inclination defining voltage values for minimizing fluctuation of inclination of each of the plurality of voltage wave-forms found in the second process.