To provide a constant current circuit which is capable of not only acquiring characteristics of various sorts of electric circuits even before a trimming adjustment is carried out, performing the trimming adjustment based upon the acquired characteristics, performing trimming processes to both the constant current circuit and a load collectively, and performing an adjustment of a constant current with high precision, but also capable of reducing a total number of manufacturing steps so that a production cost can be lowered, as compared with that of a conventional constant current circuit.A constant current circuit of the present invention includes: a current output portion including a first transistor for causing a reference current to flow and a second transistor for causing an output current with respect to a load to flow, the first transistor and the second transistor connected with each other through a current mirror connection; a depletion transistor connected in series with the first transistor, for adjusting the reference current through trimming; a third transistor interposed between the depletion transistor and a ground point, for controlling tuning on/off of a connection between the depletion transistor and the ground point; and a first external terminal for allowing the reference current to flow through the first transistor.