The reference current source circuit (10) is provided with a current source circuit (1), a trimming fuse (3), a switching circuit (2) which connects/disconnects the current source circuit (1) and/from the trimming fuse (3), a NAND circuit (4) which controls the operation of the switching circuit (2), and a pull-down resistor (R1) which connects one input terminal of the NAND circuit (4) to a GND terminal. The NAND circuit (4) controls the operation of the switching circuit (2) upon receipt of control signals (S1 and S2) and also in accordance with a signal of the one input terminal of the NAND circuit (4) so as to connect the current source circuit (1) to the trimming fuse (3). This arrangement makes it possible to measure characteristics of a semiconductor integrated circuit after fuse trimming. In addition, it is possible to maintain the state after fuse trimming without the supply of a signal from outside. Moreover, a reference current source circuit which does not consume extra consumption current is realized.