PURPOSE: To obtain a converter which lets an output voltage respond instantaneously to changes in the frequency, by performing a frequency-voltage conversion of an AC signal inputted while an output voltage thus converted is differentiated by means of a differentiation circuit to add the voltage thus differentiated to the output voltage.

CONSTITUTION: An AC pulse signal supplied from an input terminal in is converted into an output voltage B with a frequency-voltage conversion circuit 1. The voltage B responds to changes in the frequency delayed by a delay time T by means of an integrating element contained in the circuit 1. Then, the voltage B is outputted to a differentiation circuit 3 and a differential amplifier 5. As the voltage B rises (or falls) with changes in the frequency of a signal A, the circuit 3 generates a differentiation voltage as indicated by C. The voltage C is inputted into the amplifier 5 and added to the output voltage B to obtain an output voltage D differentially amplified. This enables the correcting of a delay of the output voltage B to let the output voltage B respond instantaneously to changes in the frequency thereby achieving a higher response speed.