To obtain a lamp unit which can be safely handled by a user, and which has high cooling efficiency.

A housing 10 is provided with a shutter 22 for opening/closing an opening 21. When the lamp unit 1 is not built in a projector, the opening 21 is closed, while the opening 21 is opened when the lamp unit 1 is built in the projector. When the lamp unit 1 is built in the projector, since a shutter driving projection 31 for the lamp unit 1 is automatically moved, the shutter 22 is kept open when the lamp unit 1 is built in it. On the other hand, when detaching the lamp unit 1, the shutter driving projection 31 is moved by spring force in a direction to close the shutter 22.