An object is to provide a method for preventing the occurrence of variations in time resolution by providing a calibration process to a TDC at the time of start up and further preventing the increase in circuit scale by reducing the redundancy of delay elements. A calibration of a multiphase oscillator TDC and a vernier TDC is carried out at the time of power-on. In the calibration, a timing input to be input to the vernier TDC is selected from output signals of DCCO based on a reference clock. Also, data is defined as an output signal which is adjacent to the output signal of DCCO mentioned above and proceeds in phase, and the delay therebetween is derived. By repeating it to all of the output signals, the one cycle of the output signal of DCCO is derived.