To provide a constant voltage circuit having a high PSRR.

A current source 10 generates a reference current Iref. The first transistor M1 is a depletion type MOSFET with one terminal connected to the current source 10, and with gate sources thereof connected to each other. The second transistor M2 is an enhancement type MOSFET with one terminal connected to the other end of the first transistor M1, and with the other terminal connected to a fixed voltage terminal, with gate drains thereof connected to each other. The third MOSFET is an enhancement type P-channel MOSFET with one terminal connected to the current source 10, with the other terminal connected to the fixed voltage terminal, and with the gate connected to a connection point N between the first transistor M1 and the second transistor M2. The constant voltage circuit 100 outputs a voltage corresponding to at least one of a gate voltage of the third transistor M3 and a source voltage thereof.