There is provided a constant current circuit having a current characteristic satisfactory in a high voltage circuit while being low in manufacturing cost. The constant current circuit includes a high breakdown-voltage depletion type NMOS transistor and a low breakdown-voltage depletion type NMOS transistor connected in series between a first terminal and a second terminal. The low breakdown-voltage depletion type NMOS transistor includes a first depletion type NMOS transistor and a second depletion type NMOS transistor connected in series. The high breakdown-voltage depletion type NMOS transistor has a gate connected to a connecting point of the first depletion type NMOS transistor and the second depletion type NMOS transistor.