A projection display device permits extension of a space for mounting an electronic component on a control circuit substrate. The projection display device includes a control circuit substrate on which a control circuit is mounted for controlling driving of each of apparatuses in the device according to the input operation signal from an external light receiving unit; and a signal transmission circuit comprising a light emitting element and a light receiving element and provided in a conduction passage on the circuit substrate. The control circuit substrate includes a first circuit substrate on which the control circuit is mounted, and a second circuit substrate provided opposite to the first circuit substrate, and to which the operation signal is input from the external light receiving unit. The light receiving element and the light emitting element are provided on the first circuit substrate and the second circuit substrate, respectively.