An object is to improve a trap effect to trap ignition fuel gas supplied to a pre-combustion chamber and reduce an amount of non-combusted ignition fuel gas flowing out of the pre-combustion chamber to suppress a decrease in combustion efficiency. A pre-combustion-chamber type gas engine includes: a pre-combustion chamber Sr disposed on a cylinder head portion 10; a spark plug 20 disposed on an upper part of the pre-combustion chamber Sr; a pre-combustion-chamber gas supply mechanism configured to supply ignition fuel gas “g” to the pre-combustion chamber Sr via gas supply channels for the pre-combustion chamber 22a and 22b with an opening on an upper part of the pre-combustion chamber Sr; and a check valve 24 disposed in the gas supply channel 22b for the pre-combustion chamber. The opening of the gas supply channel 22a for the pre-combustion chamber is disposed on a lower surface of a cover member 16 forming the pre-combustion chamber Sr or on an upper section of a side wall of a pre-combustion-chamber member 14, the opening facing in a tangent direction of a side-wall inner peripheral surface 14a of the pre-combustion-chamber member 14. The ignition fuel gas “g” supplied to the pre-combustion chamber Sr forms a swirl flow s1 which swirls about a longitudinal axis x of the pre-combustion chamber Sr inside the pre-combustion chamber Sr.