Abstract: The invention relates to a device for a prechamber unit (10) of a gas engine, comprising a prechamber unit (10) in the form of an elongated body (12) arranged to be placed in an upper part of the engine's cylinder, and where the elongated body (12) comprises a prechamber gas valve (20) and an ignition means (22) arranged side by side, and one or more channels (24) for supply of fuel gas via the prechamber gas valve (20) to a prechamber (26) in a lower part of the elongated body (12). Said prechamber (26) comprises further in the axial direction, an elongated cavity (28) with nozzles (30) placed at the end for supply of ignited fuel gas to the engine's cylinder with the help of the ignition means (22). The elongated cavity (28) in the prechamber (26) is divided into several connected, and in cross-section, graduated or tapered cavities (28a, 28b, 28c), where an uppermost cavity (28a) is widest in the cross-sectional direction and a bottom cavity (28c) is narrowest in the cross-sectional direction.