In an endoscope system that obtains a captured image inside of a body cavity by use of an insertion unit of an endoscope apparatus which is inserted into the body cavity of a subject, an oscillator outputs an oscillation pulse signal, and receives a reflected pulse signal. A transmission line is provided along the insertion unit near an envelope of the insertion unit, and transmits a pulse signal output from the oscillator. A time calculating unit and an insertion length calculating unit obtain a time difference between the oscillation pulse signal and the reflected pulse signal on the basis of the oscillation pulse signal output by the oscillator and the reflected pulse signal received by the oscillator, and calculate an insertion length of the insertion unit on the basis of the obtained time difference.