PURPOSE: To make additional cabling or mounting work unnecessary, by supplying a power source from an indoor distribution line on which a data signal is superposed, and using a room light which emits light on which a data signal component is superposed as a light transmission part.

CONSTITUTION: The data signal inputted to an indoor distribution line modem 1 via a data transmission cable is superposed on the AC line of the indoor distribution line in the indoor distribution line modem 1. And since the data signal component is superposed on the light emitted from the room light 2∼4 to which the power source is supplied from the indoor distribution line 11 on which the data signal component is superposed, the data signal can be reproduced at the light receiving parts 5∼7 by receiving the light at the light receiving parts 5∼7, and discriminating the data signal component.