A current source circuit includes a reference current source circuit; a reference voltage source circuit generating a voltage proportional to a thermal voltage based on the reference current; a first transistor connected between the reference voltage source circuit and the second power supply voltage and through which a first current flows; a second transistor which has a gate applied with a voltage as a result of addition of the voltage generated by the reference voltage source circuit and a voltage between a source and a drain of the first transistor and through which a second current flows; a current source supplying a third current of a current value proportional to that of the first current; and a third transistor through which a difference current between the second current and the third current flows. An output current is supplied based on the difference current.