Provided is a head-up display device wherein in a state where a light-receiving unit is connected to a control substrate, a lid can be easily mounted to a case. Housed in a case of a head-up display device are a substrate for controlling a projector and a reflection unit for reflecting light projected thereon by the projector. The reflection unit is configured to have a reflecting mirror that is held by a holder, while the substrate is connected, via a connection member, with a light-receiving unit for detecting light from outside. The light-receiving unit is configured to have a light-receiving sensor that is held by a sensor holding part. The sensor holding part for holding the light-receiving sensor is held by the holder.