A fastening tool comprising: a housing comprising a substantially cylindrical body part and a handle part extending from the body part in a substantially perpendicular direction; an air plug arranged on an end part of the handle part which is separated from the body part, wherein the air plug is configured to be supplied a compressed air; an accumulator chamber that is configured to be a part of the housing and accumulates the compressed air; a piston that reciprocates in a cylinder due to the compressed air; a driver blade that is connected to the piston and drives a fastener; a nose member having an injection port for injecting the fastener; a push lever that moves to a first position along the nose member when causing a leading end of the injection port to move in a pressing direction toward a driven material, and is located at a second position when the leading end of the injection port is not pressed to the driven material; a trigger that actuates a switch mechanism (30, 40) which controls air discharge of the accumulator chamber, wherein in a state that the push lever is moved to the first position and the trigger is pulled, by communicating the accumulator chamber with an upper chamber of the piston, the compressed air in the accumulator chamber flows into the cylinder and a strike is performed accordingly; and the fastening tool comprising a relief valve mechanism that has a control valve of a discharge pathway and an opening and closing valve of an inflow pathway from the air plug to the accumulator chamber, characterised in that the control valve is configured to discharge at least a portion of the compressed air to an outside, and the opening and closing valve is configured to close the inflow pathway, and the control valve and the opening and closing valve are controlled by the compressed air by pulling the trigger when the push lever is in the second position. a housing comprising a substantially cylindrical body part and a handle part extending from the body part in a substantially perpendicular direction; an air plug arranged on an end part of the handle part which is separated from the body part, wherein the air plug is configured to be supplied a compressed air; an accumulator chamber that is configured to be a part of the housing and accumulates the compressed air; a piston that reciprocates in a cylinder due to the compressed air; a driver blade that is connected to the piston and drives a fastener; a nose member having an injection port for injecting the fastener; a push lever that moves to a first position along the nose member when causing a leading end of the injection port to move in a pressing direction toward a driven material, and is located at a second position when the leading end of the injection port is not pressed to the driven material; a trigger that actuates a switch mechanism (30, 40) which controls air discharge of the accumulator chamber, wherein in a state that the push lever is moved to the first position and the trigger is pulled, by communicating the accumulator chamber with an upper chamber of the piston, the compressed air in the accumulator chamber flows into the cylinder and a strike is performed accordingly; and the fastening tool comprising a relief valve mechanism that has a control valve of a discharge pathway and an opening and closing valve of an inflow pathway from the air plug to the accumulator chamber, characterised in that the control valve is configured to discharge at least a portion of the compressed air to an outside, and the opening and closing valve is configured to close the inflow pathway, and the control valve and the opening and closing valve are controlled by the compressed air by pulling the trigger when the push lever is in the second position.