Provided is a constant current circuit in which an enhancement N-channel transistor can operate in a weak-inversion state even at high temperatures. A constant current circuit includes a current mirror circuit, a constant-current generation block circuit, and an off-leak circuit, wherein the off-leak circuit is constituted by a first enhancement N-channel transistor having a gate and a source connected to an earth terminal and a drain connected to an output of the constant current circuit. This suppresses an increase in a gate-to-source voltage of the enhancement N-channel transistor which generates a constant current, thereby maintaining its operation in a weak-inversion state.