A nail gun including: a gun body; a power module disposed in said gun body, and configured to perform a nail-driving operation in which said power module output power to strike a nail; and a muzzle module mounted to said gun body, and including a nail exit opening and a contact arm, said contact arm having an abutment front end, and being resiliently maintained at a normal position, said contact arm being operable to move in a nail-exit direction away from the normal position such that said abutment front end projects relative to said nail exit opening; said nail gun further includes a switchable trigger module operable to activate the nail-driving operation for firing the nail via said nail exit opening, said switchable trigger module including a transmission unit, a trigger arm unit and a trigger unit, said transmission unit including a transmission member that is connected to said contact arm, said trigger arm unit abutting against said transmission member at least in a normal state, said trigger unit including a trigger member that is pivoted to said gun body, characterized in that said trigger unit is movable relative to said gun body, and that the nail gun further comprises a blocking member that is mounted to said trigger member, said trigger member interacting with said trigger arm unit, and being operable to move between a sequential firing position and a repetitive firing position, wherein when said trigger member is at the sequential firing position and when said trigger member is depressed with said abutment front end of said contact arm not being blocked, said trigger arm unit being configured to push said transmission member to move said contact arm away from the normal position in the nail-exit direction, and said blocking member being configured to block said trigger arm unit so as to prevent said trigger arm unit from moving in a direction opposite to the nail-exit direction, such that the nail-driving operation is prevented from being activated by operation of said contact arm. a gun body; a power module disposed in said gun body, and configured to perform a nail-driving operation in which said power module output power to strike a nail; and a muzzle module mounted to said gun body, and including a nail exit opening and a contact arm, said contact arm having an abutment front end, and being resiliently maintained at a normal position, said contact arm being operable to move in a nail-exit direction away from the normal position such that said abutment front end projects relative to said nail exit opening; said nail gun further includes a switchable trigger module operable to activate the nail-driving operation for firing the nail via said nail exit opening, said switchable trigger module including a transmission unit, a trigger arm unit and a trigger unit, said transmission unit including a transmission member that is connected to said contact arm, said trigger arm unit abutting against said transmission member at least in a normal state, said trigger unit including a trigger member that is pivoted to said gun body, characterized in that said trigger unit is movable relative to said gun body, and that the nail gun further comprises a blocking member that is mounted to said trigger member, said trigger member interacting with said trigger arm unit, and being operable to move between a sequential firing position and a repetitive firing position, wherein when said trigger member is at the sequential firing position and when said trigger member is depressed with said abutment front end of said contact arm not being blocked, said trigger arm unit being configured to push said transmission member to move said contact arm away from the normal position in the nail-exit direction, and said blocking member being configured to block said trigger arm unit so as to prevent said trigger arm unit from moving in a direction opposite to the nail-exit direction, such that the nail-driving operation is prevented from being activated by operation of said contact arm.