Disclosed herein is an apparatus that includes: a data terminal; a first output transistor connected between the data terminal and a first power line supplying a first power potential; a first tristate circuit including an output node connected to a control electrode of the first output transistor, a first pull-up transistor configured to drive the output node to a first logic level, and a first pull-down transistor configured to drive the output node to a second logic level; and a second tristate circuit including an output node connected to the control electrode of the first output transistor, a second pull-up transistor configured to drive the output node to the first logic level, and a second pull-down transistor configured to drive the output node to the second logic level. The second pull-up and pull-down transistors have a different threshold voltage from the first pull-up and pull-down transistors.