An impedance calibration circuit is disclosed, which relates to a technology for improving precision of pad resistance. The impedance calibration circuit includes: a first On Die Termination (ODT) circuit selected by a first selection signal, configured to tune its own resistance using a first code signal, and output a first resistance value to an output terminal; and a second ODT circuit selected by a second selection signal, configured to tune its own resistance using a second code signal, and output a second resistance value to the output terminal.