To provide a device to be safely and easily used as a tandem bicycle by installing a connector in two bicycles for an adult and a child or to be used as a trailer by installing one bicycle and a connector.

A front arm 6 and a rear arm 7 made of aluminum are connected to each other through an angle adjustable joint 11, and fixed by an angle adjusting screw 2 and a joint stopper screw 3. A bracket 1 is installed in four movable joint pins 4 previously installed in a bicycle to be connected, and a fall preventing pin 9 is inserted, and locked by a rubber ring 13. In order to correct a difference of tire diameter between the front and the rear bicycles, the rear arm 7 is adjusted to be parallel with the ground by the lock pin 4 and the angle adjusting pin 2.