A jitter detecting apparatus wherein the jitter detection has been improved. This jitter detecting apparatus comprises a receiving circuit (1) that receives a signal; a determining circuit (3) that determines, based on the signal amplitude, a signal part of the received signal to be used for jitter detection; and a jitter detecting circuit (5) that detects, based on the determined signal part, a jitter related to the signal. The determining circuit (3) may include a first threshold value setting circuit that generates a first threshold value; a second threshold value setting circuit that generates a second threshold value; and an interval signal generating circuit that uses the first and second threshold values to generate an interval signal. The jitter detecting circuit (5) may include a signal part detecting circuit that detects the signal part by responding to the received signal in accordance with the terminal signal.