An object is to provide a precombustion-chamber gas engine in which occurrence of knocking is restricted. The precombustion-chamber gas engine includes: a cylinder; a cylinder head; a piston delimiting a main combustion chamber with the cylinder head; a precombustion-chamber cap delimiting a precombustion chamber inside thereof and including a plurality of nozzle holes through which the precombustion chamber is in communication with the main combustion chamber; an intake valve for opening and closing an intake port that opens on the cylinder head; and an exhaust valve for opening and closing an exhaust port that opens on the cylinder head. In a planar view where the cylinder head is seen from below, there are at least one intake-side nozzle hole and at least one exhaust-side nozzle hole, and a total nozzle-hole area of the at least one intake-side nozzle hole is larger than that of the at least one exhaust-side nozzle hole.