The invention provides a current source circuit. The current source circuit comprises an amplifier, a first transistor, a second transistor and a first resistor, wherein the positive-going input end of the amplifier is an analog signal input end, and the reverse input end of the amplifier is a voltage signal feedback end, the reverse input end is connected with the current output end of the firsttransistor, and the output end is connected with the input end of the first transistor; the current output end of the first transistor is grounded through the first resistor, and the input end of thesecond transistor is a pulse signal input end; the output end of the second transistor is connected with the reverse input end of the amplifier. According to the current source circuit, the output ofa current source can be cut off instantly, so that the purpose of pulse output is achieved; in addition, due to the fact that the analog input end is free of a chopper circuit, the current source circuit can work under extremely low input voltage, and therefore the current source circuit can obtain wide-range pulse current output under the condition that the sampling resistance is unchanged.