A constant current circuit that generates a constant output current corresponding to an input voltage, comprises a differential amplifying unit to which the input voltage and a feedback voltage to be compared therewith are applied, the differential amplifying unit outputting a differential voltage, a first transistor with a first control electrode to which the differential voltage is applied, a first diode element that is connected to a power-supply side electrode of the first transistor, one or a plurality of second transistors that generates the output current, a feedback voltage conversion block that converts the duplicated current of the diode current flowing through the second transistor into the feedback voltage, and a constant current loading unit that is connected to a ground side electrode of the first transistor, the constant current loading unit making a voltage change in the ground side electrode follow a voltage change in the first control electrode.