A connection device to which a relay connector is applied includes relay terminals that have first connection portions capable of being elastically deformed along a first direction, second connection portions capable of being elastically deformed along the first direction, and coupling portions connecting the first and second connection portions, and are formed integrally with the first and second connection portions, and the coupling portions, and a holding unit that holds the relay terminal and has reaction force receiving portions supporting the coupling portions with such positional relation that first counterpart terminals are capable of being connected to the first connection portions from one side in the first direction and second counterpart terminals are capable of being connected to the second connection portions from the other side in the first direction and receiving reaction forces with elastic deformation of the first and second connection portions.