A decoupling capacitor is coupled to a sense power supply line with respect to a sense amplifier circuit group, and the sense power supply line is selectively coupled with a power supply node in response to an operation mode of a sense amplifier. In a sensing operation, the potential of a bit line is determined by redistribution of charges between the decoupling capacitor and a load capacitor of the bit line. Refresh characteristics is improved without increasing a sense current and showing down the sensing operation.