To provide a signal measuring circuit which can realize a normal output of a PWM signal by an inexpensive means, and an imaging apparatus by an electrophotographic system with the signal measuring circuit.

In the measuring circuit 100 for PWM signals, a delay circuit 1 delays a reference clock signal by every minute time within one cycle and sequentially outputs delay signals. Signal value detecting circuits 6a and 6b detect a signal change of the PWM signal by the delay signals outputted from the delay circuit 1. A calculating circuit 8 calculates a measured value of a pulse width of the PWM signal from the result of the detected signal change of the PWM signal, and a measured value of a phase relation between the reference clock signal and the PWM signal. A comparator 9 calculates a difference between an expected value and the measured value of each of the pulse width and the phase relation, and minute variable delay circuits 10 and 11 and a PWM data correcting circuit 12 correct the PWM signal based on the differences.