Gas internal combustion type nailing machine

The present gas internal combustion type nailing machine is provided with: a striking cylinder (5) for slidably accommodating a striking piston (6) therein; a combustion chamber (11) formed in an upper side and capable of being opened and closed; a compressor (25) for supercharging compressed air into the combustion chamber; a fuel supply device (19) for supplying a fuel gas into the combustion chamber; and a safety device for preventing the nailing machine from being driven for ignition when the supercharge pressure of the compressed air exceeds a set pressure value; and a switch (S) configured to be turned ON by operating a trigger (40) and to ignite the mixed gas within the combustion chamber, wherein the safety device comprises a cylinder mecahnism (47) configured to operate to prevent the switch from turning ON based on a pressure in the combustion chamber which exceeds the set pressure value.