A semiconductor memory device having high integration, low power consumption and high operation speed. The memory device includes a sense amplifier circuit having plural pull-down circuits and a pull-up circuit. A transistor constituting one of the plural pull-down circuits has a larger constant than that of a transistor constituting the other pull-down circuits, for example, a channel length and a channel width. The pull-down circuit having the larger constant transistor is activated earlier than the other pull-down circuits and the pull-up circuit, which are activated to conduct reading. The data line and the earlier driven pull-down circuit are connected by an NMOS transistor and the NMOS transistor is activated or inactivated to control the activation or inactivation of the pull-down circuit.