Provided is a half mirror which is used for a windshield constituting a head up display, and in which a feeling of glare is suppressed, and a boundary between a region which selectively reflects visible light and a region which reflects visible light is made inconspicuous. The half mirror has a reflection layer including a non-reflection region which does not reflect visible light, a reflection region which selectively reflects visible light, and a mixed region which is provided between the regions and in which a non-reflection portion which does not reflect visible light and a reflection portion which selectively reflects visible light are mixed, and in the mixed region, an area of the reflection portion is gradually increased from the non-reflection region toward the reflection region.