The present invention provides a laser unit using a seal member whose central and peripheral portions will not affect each other to produce strain during mounting and which can be handled as a single component.In the laser unit 100 according to the present invention, a central portion 41 and a peripheral portion 42 of a seal member 40 used are separated from each other by slits 43. Therefore, when the seal member 40 is mounted, the central and peripheral portions will not affect each other to increase strain. In addition, because the central and peripheral portions are connected to each other at several points by bridging portions 44, the seal member 40 can be handled as a single component, which is very convenient.