In the radio communication control of the slave telephone set with a unit ID in one-to-one correspondence to one slave telephone set, in order to assign two or more communication channels to one slave telephone set for radio communication, a plurality of unit IDs are registered in each slave telephone set are also registered in the master telephone set. The projector includes: a light source device; an electro-optic device that modulates light emitted from the light source device; two polarizers that are disposed respectively on a light incoming side and a light outgoing side of the electro-optic device; and a projection optical system that projects light output from the electro-optic device. The wireless communication device, when used by itself, operates as a monopole antenna in which the plane conductor functions as a ground and the coil conductor functions as a radiation element.