An impactor according to an embodiment of the present invention comprises an adapter detachably coupled to a rotary power tool, wherein the adapter includes: a case part; a tool coupling part receiving a rotational force from the rotary power tool; a first rotating part rotating in association with rotation of the tool coupling part in only one direction among rotation directions of the tool coupling part; a striking part transfer part rotating in association with rotation of the first rotating part; a striking part which is moved, while compressing a first spring, in a first direction by rotation of the striking part transfer part and then moved in a second direction opposite to the first direction by a restoring force of the first spring; and a force transfer part moved in the second direction by contact with the striking part.