It is desirable to provide a technology capable of improving reliability in light transmission and convenience at the time of connecting a transmission device to a cable with a simple circuit configuration. A transmitting device is provided which includes a connector receptacle unit connected to an optical-electrical composite cable, in which the connector receptacle unit includes a first electrode group, a second electrode group provided at a position rotated from the first electrode group by 180 degrees about a center of a main body of the connector receptacle unit as a reference, a first connection unit group for transmitting optical signals, and a second connection unit group for transmitting optical signals provided at a position rotated from the first connection unit group for transmitting optical signals by 180 degrees about the center of the main body of the connector receptacle unit as a reference.