An apparatus includes a first terminal configured to communicate data with an outside of the apparatus, a second terminal configured to receive a first power source potential, a third terminal configured to receive a second power source potential lower than the first power source potential, a fourth terminal configured to be coupled to a calibration resistor, an output buffer including first to third nodes coupled to the first to third terminals respectively, and a replica circuit including fourth and fifth nodes coupled to the second and third terminals respectively, and sixth node coupled to the fourth terminal.