An electrical connector comprising: a housing main body including a central cylinder provided in a central portion of the housing main body, and an outer cylinder disposed outside the central cylinder to surround the central cylinder with a gap provided therebetween; and a terminal holder that holds a plurality of connection terminals and is inserted into an inside of the central cylinder inside the housing main body from a rear of the housing main body, wherein a mating electrical connector including built-in mating connection terminals facing the connection terminals is configured to be fitted into a front of the housing main body, so that electrical connection is performed through the connection terminals and the mating connection terminals, and a housing of the mating electrical connector is configured to be inserted between the central cylinder and the outer cylinder, a first seal portion made of a synthetic rubber is formed on an outer surfaces of the central cylinder, and the first seal portion (ij) is configured to be in contact with the housing of the mating electrical connector to realize a waterproof structure between the outer surface and the housing, characterized in that the central cylinder is provided with a communication hole passing through both an inner surface and the outer surface of the central cylinder, a second seal portion made of a synthetic rubber which communicates with the first seal portion through the communication hole and is integrated with the first seal portion is formed on the inner surface of the central cylinder, and the second seal portion is in contact with the terminal holder to realize a waterproof structure between the inner surface and the terminal holder. a housing main body including a central cylinder provided in a central portion of the housing main body, and an outer cylinder disposed outside the central cylinder to surround the central cylinder with a gap provided therebetween; and a terminal holder that holds a plurality of connection terminals and is inserted into an inside of the central cylinder inside the housing main body from a rear of the housing main body, wherein a mating electrical connector including built-in mating connection terminals facing the connection terminals is configured to be fitted into a front of the housing main body, so that electrical connection is performed through the connection terminals and the mating connection terminals, and a housing of the mating electrical connector is configured to be inserted between the central cylinder and the outer cylinder, a first seal portion made of a synthetic rubber is formed on an outer surfaces of the central cylinder, and the first seal portion (ij) is configured to be in contact with the housing of the mating electrical connector to realize a waterproof structure between the outer surface and the housing, characterized in that the central cylinder is provided with a communication hole passing through both an inner surface and the outer surface of the central cylinder, a second seal portion made of a synthetic rubber which communicates with the first seal portion through the communication hole and is integrated with the first seal portion is formed on the inner surface of the central cylinder, and the second seal portion is in contact with the terminal holder to realize a waterproof structure between the inner surface and the terminal holder.