An impact tool includes a motor, an impact mechanism, an output shaft, a control unit, and an angular lead measurer. The impact mechanism includes a hammer and an anvil. The anvil rotates upon receiving impacting force from the hammer. The angular lead measurer measures an angular lead in rotation of the anvil over the hammer. The control unit changes, according to the angular lead measured by the angular lead measurer, a control mode for controlling the rotational velocity of the output shaft from one of a plurality of modes to another.