Abstract: The breech block for pneumatic shooting device is utilized in weapons for expelling solid-state bodies or marking pellets. It has a simplified and easy for maintenance construction ensuring long term exploitation and minimum fluid consumption for one shot. The breech block comprises a housing 1 in which a barrel 2 is mounted. A step-shaped cylindrical bore is formed in the housing 1, and a piston 4 having two parts 9 and 10 of different diameters is placed in the bore. The step-shaped bore in the housing 1 has a portion 13 which diameter is greater than the diameter of the rear part 10 of the piston 4. The piston 4 is provided with an axial passage 14, the rear end of which being connected to radial openings 8 formed at the rear part 10 of the piston 4.