A driving tool includes a chamber to store compressed air and a relief valve in communication with the chamber. The relief valve includes an inflow channel communicating with the chamber and an outflow channel with a larger diameter formed at a downstream side of the inflow channel. A valve stem moves along the inflow channel. An O-ring to seal the inflow channel is attached in an annular groove of the valve stem. Air release channels are defined in the valve stem. Each air release channel includes an inlet that opens to an inner circumferential chamber and an outlet that opens to the outflow channel to allow the compressed air to be discharged from the inner circumferential chamber to the outflow channel when the O-ring moves toward the outflow channel and moves beyond the inflow channel due to the internal pressure of the chamber.