PURPOSE: To attain the inexpensive method with high accuracy by using a ring oscillator oscillating a timing delay quantity and detecting the delay quantity from the change in the oscillated frequency so as to eliminate the need for a linear change in the delay of a delay adjusting device.

CONSTITUTION: A ring oscillation control section 6 building-in a frequency counter is provided between an output of a delay adjusting device 4 and an input of the device 4 via a switch 5, an output of the delay adjusting device 4 is fed back to the input to form a ring oscillation circuit, and its oscillated frequency is measured by a frequency counter to calculate the timewise delay accurately based on the measurement. At this time, to feed back the output of the delay adjusting device 4 to its input, it has only to be executed with further delay or pulse width shaping as required. Further, since the switch 5 is not normally thrown to the position of the frequency divider 3, the feedback path is used only when the delay of the delay adjusting device 4 is measured.