Proposed is an iridium alloy catalyst having reversible catalytic activity for an oxygen evolution reaction (OER), a hydrogen evolution reaction (HER), and a hydrogen oxidation reaction (HOR) by including an iridium alloy including iridium (Ir) and nickel (Ni). The iridium alloy catalyst according to the present disclosure is rapidly converted to an iridium alloy catalyst in an oxide form and an iridium alloy catalyst in a metallic form according to applied voltage by controlling its crystallinity. Thus, even in case an oxide layer is formed after the OER, the oxidation layer disappears during the HER and HOR and the properties of an iridium metal catalyst remain, thereby maintaining HER/HOR performance.