An impact driver includes a hammer that is rotated by a motor and an anvil configured to be struck by the hammer to rotate the anvil about a rotational axis. A hammer case houses the hammer. Two or more bearings are provided inside the hammer case and support the anvil. To inhibit vibration of the anvil during operation, the bearings may be differing types, such as a regular ball bearing and an angular contact ball bearing, and/or the bearings may have different inner and/or outer diameters. A contact member, such as an O-ring, may be disposed in an insertion hole of the anvil to reduce vibrations that are transmitted to the tool bit.