To obtain a circuit capable of extending a pulse width by allowing first and second edge detecting circuits to detect the respective rising and falling edges of two pulse signals, starting integrating operation when the first edge detecting circuit detects an edge and finishing integrating operation when the second edge detecting circuit detects an edge.

One side pulse signal inputted to the clock input terminal CK of a flip-flop circuit FF1 through a terminal 7 varies from a low level to a high level. By this step, an output from the noninverted output terminal Q of the circuit FF1 is varied from the low level to the high level by synchronizing with the rising edge of the pulse signal. Then, switches SW1 and SW3 are opened to boost the output voltage of an arithmetic amplifier OP1 according to a time constant decided by the product of the capacitance of a capacitor C1 and the resistance value of a resistor R1.