A connector having a plug connected to an antenna through a coaxial cable and a receptacle. The plug includes a cylindrical shell, a pin contact, and an insulative pin contact holder provided inside the shell. The receptacle includes a first receptacle housing having a shell-receiving hole and a second receptacle housing provided inside the shell-receiving hole and having a pin contact-receiving hole. A first protrusion is formed in a distal end of the pin contact holder. A first reentrant in which the first protrusion is to be fitted is formed in a distal end of the second receptacle housing. The present invention can prevent the connection of external antennas of other manufacturers to the receptacle because the first protrusion and first reentrant are specified in shape. Also, the plug can be readily connected to the receptacle because the plug can be connected to the receptacle independently of the posture of the plug.