To securely ignite and burn fuel gas even if the injection pressure of the fuel gas fluctuates.

This internal combustion engine injecting the fuel gas into the cylinder comprises a cylinder 1 incorporating a piston 2, an injection nozzle 3 injecting the pressurized fuel gas into the cylinder 1, and an ignition plug 4 igniting the jet flow of the fuel gas. In the internal combustion engine, the ignition plug 4 directly ignites the jet flow of the fuel gas by spark-discharging at a timing when the fuel gas is injected from the injection nozzle 3 into the cylinder 1. Also, the internal combustion engine is formed such that a decelerated impact part 10 allowing the fuel gas injected from the injection nozzle 3 to impact thereon is disposed in a hollow part inside the cylinder 1 apart from the inner surface of the cylinder. In the internal combustion engine, the fuel gas injected from the injection nozzle 3 is impacted on the decelerated impact part 10 to decelerate the flow velocity, and the ignition plug 4 ignites the jet flow decelerated by the decelerated impact part 10.