A compact sense amplifier circuit for amplifying reading signal of an EPROM includes a bit line connected to cells of the EPROM and a transistor circuit for connecting a DC power source to the bit line. The transistor circuit includes a read circuit, a write circuit, a first path for passing current when a read signal for reading one of the cells that is not written is applied to the read circuit and a second path for passing current when a read signal for reading one of the cells that is written is applied to the read circuit. The first path and the second path are arranged to pass the same amount of current, thereby reducing sensor noises.