A pre-chamber unit (1) of the cylinder of a combustion engine, comprises a pre-chamber (2) and an elongated nozzle chamber (3) connected thereto, and a number of orifices (4) is provided at its oneend for connecting the pre-chamber to the main combustion space(5) of the cylinder. The nozzle chamber (3) comprises a part (3b) that is enlarged at least at the position of the orifices (4), its diameter in the transversal direction of the nozzle chamber (3) being larger than that of the part (3a) between the orifices and the pre-chamber.