A focal point controlling section is configured and arranged to control a focal point of the laser beam outputted from a laser oscillator to selectively focus the laser beam on a surface of a workpiece. A laser irradiation position moving section is configured to move a laser irradiation position at which the laser beam strikes on the surface of the workpiece. A control unit is configured to change a heat amount imparted on the surface of the workpiece to switch between a welding state and a non-welding state by controlling at least one of the focal point controlling section and the laser irradiation position moving section while controlling the laser oscillator to continuously output the laser beam before and after switching between the welding state and the non-welding state.