Multipolar electrical connector

A multipolar electrical connector which uses a single-head plug as a counter connector, said single-head plug including:

• a pole shaft in which center poles are disposed in plural positions in an axial direction;
• and at least one peripheral pole which is opposed to an outside of a root of the said pole shaft with being separated from the root of said pole shaft by a distance, wherein said connector includes:
• a body comprising an insertion space for said pole shaft;
• a plurality of predetermined contact pieces attached to said body and comprising predetermined contacts which are to be in contact with said center poles other than said center pole in the root of said pole shaft that is inserted into said insertion space, respectively;
• a cylindrical boss portion which protrudes from a front end of said body, and which forms an insertion/extraction port communicating with said insertion space;
• a plate-like first additional contact piece which is placed in a placement position for said first additional contact piece, said placement position being formed in at least one position of an outer peripheral side of said boss portion;
• a first additional contact which is disposed on said first additional contact piece, and which is to be in contact with said peripheral pole disposed in said counter connector;
• a second additional contact piece which is placed in a placement position for said second additional contact piece, said placement position being formed in at least one position of an inner peripheral side of said boss portion;
• and
• a second additional contact which is disposed on said second additional contact piece, and which is to be in contact with said center pole in the root of said pole shaft of said counter connector.