An impact device comprising: a percussion piston, which is an elongated object and provided with at least one first working pressure surface for moving the percussion piston in an impact direction by means of pressure medium, and at least one second working pressure surface for moving the percussion piston in a return direction, and the percussion piston comprising a front end facing towards the impact direction and a rear end facing towards the return direction; a bush, which is an elongated object and provided with an outer surface and an inner surface; and wherein the percussion piston is located inside the bush; the outer surface of the bush being provided with support surfaces for supporting the bush, whereby the bush may be supported to a device frame separate from the impact device; at least one bearing for supporting the percussion piston to the bush; and pressure medium ducts for connecting the working pressure surfaces (24, 25) of the percussion piston to a pressure medium system; characterized in that the percussion piston comprises at least one pull shoulder, which comprises an outer diameter and further a first counter surface facing towards the return direction; the inner surface of the bush is provided with at least one counter section located between the pull shoulder and a rear end of the bush, and the counter section comprises an inner diameter and further a second counter surface facing towards the impact direction; the outer diameter of the pull shoulder is greater than the inner diameter of the counter section; the rear end of the percussion piston is provided with a fastening point allowing a fitting tool to be connected to the rear end of the percussion piston; and the first counter surface of the pull shoulder and the second counter surface of the counter section are allowed to abut when the percussion piston is pulled in the return direction. a percussion piston, which is an elongated object and provided with at least one first working pressure surface for moving the percussion piston in an impact direction by means of pressure medium, and at least one second working pressure surface for moving the percussion piston in a return direction, and the percussion piston comprising a front end facing towards the impact direction and a rear end facing towards the return direction; a bush, which is an elongated object and provided with an outer surface and an inner surface; and wherein the percussion piston is located inside the bush; the outer surface of the bush being provided with support surfaces for supporting the bush, whereby the bush may be supported to a device frame separate from the impact device; at least one bearing for supporting the percussion piston to the bush; and pressure medium ducts for connecting the working pressure surfaces (24, 25) of the percussion piston to a pressure medium system; characterized in that the percussion piston comprises at least one pull shoulder, which comprises an outer diameter and further a first counter surface facing towards the return direction; the inner surface of the bush is provided with at least one counter section located between the pull shoulder and a rear end of the bush, and the counter section comprises an inner diameter and further a second counter surface facing towards the impact direction; the outer diameter of the pull shoulder is greater than the inner diameter of the counter section; the rear end of the percussion piston is provided with a fastening point allowing a fitting tool to be connected to the rear end of the percussion piston; and the first counter surface of the pull shoulder and the second counter surface of the counter section are allowed to abut when the percussion piston is pulled in the return direction.