A sense amplifier circuit of a nonvolatile semiconductor memory device is provided. The sense amplifier circuit includes a reference voltage generator, a sensing voltage generator and a comparator. The sensing voltage generator outputs a sensing voltage to a sensing node depending on a current flowing through a data line. A load transistor supplying a current to the data line is directly connected to a clamping node. The load transistor is included in a current mirror circuit. In a read operation, a low voltage drive operation is performed and a sensing speed and power consumption are properly controlled.