PURPOSE: To measure the time interval of a specific signal among input time signals which differ in time interval speedily with high precision by deciding whether the time interval of an input time signal is within a set range or not and inputting the measured value.

CONSTITUTION: The opening of an AND gate 206 is controlled by two stages of flip-flops FF204 and FF205 which are supplied with an input time signal inputted to a gate means 202 and an inverted input time signal passed through an inverter 207 respectively according to the time interval of the input time signal. Then, a clock passed through the gate 206 is supplied to the maximum value clocking means 209 and minimum value clocking means 210 of a clocking means 210 and when it is decided whether the time interval of the input time signal is within the range between the maximum and minimum values of the time interval set by an operating means 211, the time interval measured value of the input time signal measured with high precision by a measuring means 217 by using a high-frequency clock, etc., is inputted. Therefore, many measured values need not be inputted for statistical processing, etc., and the time interval of a specific signal is measured speedily with high precision.