A current mirror circuit and a current generation circuit are connected in series between a power supply node and a ground node through a first node and a second node. Gates of transistors constituting the current mirror circuit are connected to the node that supplies an off-voltage of the transistors through a first switch, and is connected to the second node through a second switch. The second node is connected to the node that supplies an on-voltage of the transistors through a third switch. Before starting of the circuit, the first switch and the third switch are turned on while the second switch is turned off. After starting of the circuit, on and off of the first to third switches are switched.