A receptacle is provided to connect modular electronic instruments to each other. A box-shaped case has a front face having an opening for inserting a single modular electronic instrument into the box-shaped case. A first connector is disposed inside the box-shaped case to connect the single modular electronic instrument to the receptacle. A second connector is disposed on a first side face of the receptacle for connecting the receptacle to a first receptacle on the side of the first side face. A third connector is disposed on a second side face of the receptacle for connecting the receptacle to a second receptacle on the side of the second side face. A lock secures the connection with one of the first and second receptacles. A leg is disposed on the bottom face. The position of the leg is deviated only to one of the first or second side faces.