To provide an electropneumatic connection device which can prevent a connector for electropneumatic connection from being damaged even of a connection between the king pin of a trailer and the fifth wheel if a tractor comes off against one's own will, is excellent in connection reliability, and does not allow a connector on the tractor side to interfere with loading for the trailer.

A connection part 103 in the side of a tractor is disposed at the lower surface of the fifth wheel 102 of the tractor, furthermore, at a position down below the king pin 2 of a trailer, a guide rail 108 is provided, which guides a connector on the trailer side in the direction identical to the contacting/ parting direction of the fifth wheel 102 and the king pin 2. When the fifth wheel 102 comes off from the king pin 2 against one's will, an electropneumatic connection between the connectors can be separated passively by the dissociation of both the fifth wheel and the king pin.