PURPOSE: To obtain a frequency-voltage conversion circuit with fast response by combining a function generator and a sample and mold circuit so as to obtain a voltage proportional to an input frequency in one period.

CONSTITUTION: A synchronizing signal VD is given to a trigger terminal of the 1st monostable multivibrator (MV) 1, from which a set pulse is generated. The set pulse is given as the trigger input of a 2nd MV 2 and as a hold signal of a sample and hold circuit (SH) 4. In generating the set pulse, the 2nd MV 2 generates a reset pulse. A function generating circuit 3 generates a voltage represented by V=K/t (t is the elapsed time from the end of reset pulse and V is the output voltage) and is reset by the next reset pulse. The SH 4 holds the output voltage of the function generator circuit 3 at the point of time of the set pulse.