To enable the test of propagation delay time of a semiconductor integrated circuit and the judgment of pass or fail, without depending upon the change of junction temperature of the circuit.

This delay time measuring circuit is provided with a rise signal control circuit 31 determining the propagation delay time of a rise signal, a fall signal control circuit 32 determining the propagation delay time of a fall signal, and a pulse signal forming circuit 33 in which the width and the duty ratio of a forming pulse signal is determined when the output of the rise signal control circuit 31 and the output of the fall signal control circuit 32 are inputted. A ring oscillator is formed by performing feedback by inputting the output of the pulse signal forming circuit 33 in the control circuits 31 and 32. The propagation delay time of a circuit to be measured is measured by using the above circuit and measuring the duty ratio of the out put of the pulse signal forming circuit 33.