To provide a hammering tool capable of surely preventing idle- hammering phenomenon and no-hammering phenomenon.

A cylinder 2 is provided in a body casing 1. An adapter 3 is movably provided on the end part of the cylinder 2, and a tool 4 is fitted to the adapter 3. A hammer 5 is provided in the cylinder 2 movably in the axial direction, and a piston 7 to be reciprocated by a motor 6 is stored in the cylinder 2 above the hammer 5. A suction/exhaust port 2a, a first idle-hammering preventing hole 2b, a second idle-hammering preventing hole 2d, and an air adjusting hole 2c are successively made in a side wall of the cylinder 2. The opening area of the second idle-hammering preventing hole 2d is set to 1/10 to 1/3 of the opening area of the first idle-hammering preventing hole 2b.