An alignment system for use with a laser apparatus, comprising: a guide laser device (40, 40a, 40b) configured to output a guide laser beam; an adjusting mechanism (41, 41a, 41b) configured to adjust a travel direction of at least one of the guide laser beam and a laser beam from the laser apparatus; a beam path combiner (44, 44a, 44b) configured to control a travel direction of the laser beam and a travel direction of the guide laser beam to substantially coincide with each other; a first optical detection unit (45, 45a, 45b) provided downstream from the beam path combiner and configured to detect the laser beam and the guide laser beam; a first controller (48, 48a, 48b) configured to control the adjusting mechanism (41, 41a, 41b) based on a detection result of the first optical detection unit; a beam steering unit (51, 51a, 51b) provided downstream from the beam path combiner and configured to control travel directions of the laser beam and the guide laser beam; a second optical detection unit provided downstream from the beam steering unit (51, 51a, 51b) and configured to detect at least the guide laser beam; and a second controller (58, 58a, 58b) configured to control the beam steering unit (51, 51a, 51b) based on a detection result of the second optical detection unit, characterised in that the beam steering unit (51, 51a, 51b) includes a hollow optical pipe and high-reflection mirrors (50a, 52, 52a, 52b, 53, 53a, 53b), one of the high-reflection mirrors (52, 52a, 52b) is held by a mirror holder which has its position and posture adjusted through an actuator unit, and a further of the high-reflection mirrors (53, 53a, 53b) is held by a further mirror holder which has its position and posture adjusted through a further actuator unit. a guide laser device (40, 40a, 40b) configured to output a guide laser beam; an adjusting mechanism (41, 41a, 41b) configured to adjust a travel direction of at least one of the guide laser beam and a laser beam from the laser apparatus; a beam path combiner (44, 44a, 44b) configured to control a travel direction of the laser beam and a travel direction of the guide laser beam to substantially coincide with each other; a first optical detection unit (45, 45a, 45b) provided downstream from the beam path combiner and configured to detect the laser beam and the guide laser beam; a first controller (48, 48a, 48b) configured to control the adjusting mechanism (41, 41a, 41b) based on a detection result of the first optical detection unit; a beam steering unit (51, 51a, 51b) provided downstream from the beam path combiner and configured to control travel directions of the laser beam and the guide laser beam; a second optical detection unit provided downstream from the beam steering unit (51, 51a, 51b) and configured to detect at least the guide laser beam; and a second controller (58, 58a, 58b) configured to control the beam steering unit (51, 51a, 51b) based on a detection result of the second optical detection unit, characterised in that the beam steering unit (51, 51a, 51b) includes a hollow optical pipe and high-reflection mirrors (50a, 52, 52a, 52b, 53, 53a, 53b), one of the high-reflection mirrors (52, 52a, 52b) is held by a mirror holder which has its position and posture adjusted through an actuator unit, and a further of the high-reflection mirrors (53, 53a, 53b) is held by a further mirror holder which has its position and posture adjusted through a further actuator unit.