A nail gun having: a gun body including a muzzle, and an operation portion that is for activating firing operation; a safety unit including a first safety member that is movable relative to said muzzle in a lengthwise direction of said gun body, and a second safety member that is for being pushed by said first safety member to actuate said operation portion and that is movable relative to said gun body between an initial position and an actuating position, said first safety member has an abutment portion, said second safety member being distal from a rear portion of said gun body when being at the initial position, said second safety member being proximate to said rear portion of said gun body and actuating said operating portion when being at the actuating position; and an adjusting unit including a fixing member that is co-movably mounted to said second safety member, and a switch member that is disposed between said fixing member and said second safety member and that is movable relative to said second safety member in a lateral direction of said gun body between a deep-drive position and a shallow-drive position, said switch member being configured for being pushed by said first safety member so as to move said second safety member, and having a first abutment surface, and a second abutment surface that is misaligned from said first abutment surface in the lengthwise direction and that is located ahead of said first abutment surface by a length difference, said first abutment surface being aligned with said abutment portion of said first safety member when said switch member is at the deep-drive position, said second abutment surface being aligned with said abutment portion of said first safety member when said switch member is at the shallow-drive position, characterised in that when a pressing end of the first safety member is pressed against an object, the first safety member first moves toward the second safety member in the lengthwise direction by a first distance before the abutment portion of the first safety member is in contact with the first abutment surface of the switch member. a gun body including a muzzle, and an operation portion that is for activating firing operation; a safety unit including a first safety member that is movable relative to said muzzle in a lengthwise direction of said gun body, and a second safety member that is for being pushed by said first safety member to actuate said operation portion and that is movable relative to said gun body between an initial position and an actuating position, said first safety member has an abutment portion, said second safety member being distal from a rear portion of said gun body when being at the initial position, said second safety member being proximate to said rear portion of said gun body and actuating said operating portion when being at the actuating position; and an adjusting unit including a fixing member that is co-movably mounted to said second safety member, and a switch member that is disposed between said fixing member and said second safety member and that is movable relative to said second safety member in a lateral direction of said gun body between a deep-drive position and a shallow-drive position, said switch member being configured for being pushed by said first safety member so as to move said second safety member, and having a first abutment surface, and a second abutment surface that is misaligned from said first abutment surface in the lengthwise direction and that is located ahead of said first abutment surface by a length difference, said first abutment surface being aligned with said abutment portion of said first safety member when said switch member is at the deep-drive position, said second abutment surface being aligned with said abutment portion of said first safety member when said switch member is at the shallow-drive position, characterised in that when a pressing end of the first safety member is pressed against an object, the first safety member first moves toward the second safety member in the lengthwise direction by a first distance before the abutment portion of the first safety member is in contact with the first abutment surface of the switch member.