To improve precision of a pulse signal period.

In the timing of level transition when a second period voltage Vsaw2 becomes equal with a main reference voltage Vmain, a first period voltage generating circuit 74 starts a first monotonous change period during which a voltage value of a first period voltage Vsaw1 monotonously increases from 0 that is an initial value toward a voltage value of the main reference voltage Vmain. In the timing of level transition of a first main switching signal S11 when the first period voltage Vsaw1 becomes equal with the main reference voltage Vmain, a second period voltage generating circuit 76 starts a second monotonous change period during which a voltage value of a second period voltage Vsaw2 monotonously increases from 0 that is an initial value toward the voltage value of the main reference voltage Vmain.