A precombustion-chamber gas engine, comprising: a cylinder; a cylinder head disposed on a top portion of the cylinder; a piston reciprocably disposed inside the cylinder, the piston delimiting a main combustion chamber with the cylinder head; a precombustion-chamber cap disposed inside the cylinder head at the center part of the cylinder head, the precombustion-chamber cap delimiting a precombustion chamber inside the precombustion-chamber cap and including a plurality of nozzle holes (16,16a,16b) through which the precombustion chamber is in communication with the main combustion chamber; an ignition plug disposed in the precombustion chamber; an intake valve for supplying mixed air to the main combustion chamber by opening and closing an intake port that opens on the cylinder head; and an exhaust valve for discharging exhaust gas in the main combustion chamber by opening and closing an exhaust port that opens on the cylinder head, wherein fuel gas for ignition is supplied to the precombustion chamber without passing through the main combustion chamber, characterized in that, when dividing the main combustion chamber into two regions including an intake-side region having the intake port and an exhaust-side region having the exhaust port and defining at least one nozzle hole arranged to be oriented to the intake-side region as at least one intake-side nozzle hole and at least one nozzle hole arranged to be oriented to the exhaust-side region as at least one exhaust-side nozzle hole from among the plurality of nozzle holes disposed in the circumferential direction of the precombustion-chamber cap in a planar view where the cylinder head is seen from below, the number of the at least one intake-side nozzle hole is larger than the number of the at least one exhaust-side nozzle hole, and the at least one intake-side nozzle hole and the at least one exhaust-side nozzle hole each have an identical nozzle-hole area. a cylinder; a cylinder head disposed on a top portion of the cylinder; a piston reciprocably disposed inside the cylinder, the piston delimiting a main combustion chamber with the cylinder head; a precombustion-chamber cap disposed inside the cylinder head at the center part of the cylinder head, the precombustion-chamber cap delimiting a precombustion chamber inside the precombustion-chamber cap and including a plurality of nozzle holes (16,16a,16b) through which the precombustion chamber is in communication with the main combustion chamber; an ignition plug disposed in the precombustion chamber; an intake valve for supplying mixed air to the main combustion chamber by opening and closing an intake port that opens on the cylinder head; and an exhaust valve for discharging exhaust gas in the main combustion chamber by opening and closing an exhaust port that opens on the cylinder head, wherein fuel gas for ignition is supplied to the precombustion chamber without passing through the main combustion chamber, when dividing the main combustion chamber into two regions including an intake-side region having the intake port and an exhaust-side region having the exhaust port and defining at least one nozzle hole arranged to be oriented to the intake-side region as at least one intake-side nozzle hole and at least one nozzle hole arranged to be oriented to the exhaust-side region as at least one exhaust-side nozzle hole from among the plurality of nozzle holes disposed in the circumferential direction of the precombustion-chamber cap in a planar view where the cylinder head is seen from below, the number of the at least one intake-side nozzle hole is larger than the number of the at least one exhaust-side nozzle hole, and the at least one intake-side nozzle hole and the at least one exhaust-side nozzle hole each have an identical nozzle-hole area.