PURPOSE: To provide an ac electric vehicle controlling equipment which is easy to maintain and requires no capacitance meter separately.

CONSTITUTION: The amount of charge stored in a smoothing capacitor 6 is determined by integrating the current detected by an ac current detector 12A by an integrator 16. The amount of charge determined is divided by a divider 17 by the voltage of the smoothing capacitor 6 which was detected by a dc voltage detector for controlling 13. The value then obtained is the capacitance of the smoothing capacitor 6.