Joining structure of connector

A joining structure of a connector comprising:

• one connector having a plurality of engaging portions;
• and
• another connector having the same number of engaging portions as the number of the plurality of engaging portions in the one connector, the plurality of engaging portions in the one connector and the plurality of engaging portions in the another connector being mutually corresponded so as to form a plurality of engaging pairs,
• wherein the plurality of engaging portions in the one connector and the plurality of engaging portions in the another connector respectively have shapes so that respective engaging portions can correspondingly engage with each other so as to form the plurality of engaging pairs in the case that the one connector and the another connector are joined in a proper direction, and at least one of pairs between the plurality of engaging portions in the one connector and the plurality of engaging portions in the another connector can not engage with each other in the case that the one connector and the another connector are joined in an improper direction,
• wherein the one connector has a positioning recess portion, the another connector has a positioning protruding portion, the plurality of engaging portions in the one connector have an engaging piece, and the plurality of engaging portions in the another connector have a groove portion corresponding to the engaging piece,
• and wherein as the one connector and the another connector are adapted to be joined in the proper direction, the engaging piece is pressure contacted to the side wall of the groove portion so as to be elastically deformed in a state that the positioning protruding portion rides over the side surface of the one connector so as to engage with the side surface, and then the engaging piece elastically keeps an engaging state between the positioning recess portion and the positioning protruding portion in a state that the positioning recess portion and the positioning protruding portion are engaged with each other.