PURPOSE: To attain a stable and accurate measurement for a composite cycle waveform by successively detecting intersected points crossing with an input waveform and a reference level, calculating each time interval between the 1st-2nd-3rd and (n)th-(n+1) th-(n+2)th intersected points and also calculating the detection of waveform slope and time interval at the 1st and (n)th intersected point.

CONSTITUTION: The subject device is furnished with a comparator 13 for an intersected point detecting means, subtracting devices 25, 26 for 1st subtracting means, subtracting devices 27, 28 for 2nd subtracting means, slope direction detecting circuit 29, area comparator circuits 30, 31, and subtracting device 33 for 3rd subtracting means. The time interval between the 1st-2nd, 2nd-3rd, (n)th-(n+1)th and (n+1)th-(n+2)th intersected points crossing with the input waveform and the reference level, are respectively calculated, and the differences between them are detected, then the detection is made whether the waveform between the 1st-3rd intersected points is the same as the waveform between the (n)th-(n+2)th intersected points or not by means of detecting whether the directions of input waveform slopes at the 1st and (n)th points are the same or not. By this procedure, the measurement for one cycle can be accurately performed without using an oscilloscope, etc., even for the composite cycle waveform.