An accessory includes: a detection terminal; a first power supply terminal through which a first power supply voltage is supplied; a second power supply terminal through which a second power supply voltage is supplied; a ground terminal; a ready terminal; a first clock terminal; a first data terminal; a second data terminal; a second clock terminal; a third data terminal; a first circuit to which the first power supply voltage is supplied through the first power supply terminal; and a second circuit to which the second power supply voltage is supplied through the second power supply terminal, wherein: the ground terminal is used as a ground potential for the first circuit and the second circuit; and a distance between the second clock terminal and the first power supply terminal is longer than a distance between the first clock terminal and the first power supply terminal.