An optical axis adjusting method includes a position detecting step of emitting a laser beam from a laser oscillator, applying the laser beam to a processing point, and detecting the position of the laser beam by using a position detecting unit set at the processing point, a storing step of storing the position of the laser beam as detected in the position detecting step as a reference position, and an adjusting step of operating an adjusting mechanism of each optical component holder in the case that the position of the laser beam is deviated from the reference position after performing maintenance of each optical component, thereby adjusting the position of the laser beam so that the position of the laser beam is shifted back to the reference position.