To enable to detect certainly insertion of any of the plugs for electric signal and optical signal without delay by discriminating them.

The plug insertion detection mechanism is constituted of a first sleeve spring 2, a make spring 3 adjoining this, and a second sleeve spring 4 incorporated in a housing 1 of a jack. The first sleeve spring 2 is constituted of a contact piece part 2c at the tip side folded back at the tip and an action part 2b on this side, and the action part 2b is arranged at the side along the longitudinal direction toward the plug insertion hole 1a side. The make spring 3 has its contact part 3b opposed to the contact piece 2c of the first sleeve spring 2 and is arranged on the opposite side to the plug insertion hole 1a in parallel to this. The second sleeve spring 4 has its tip contact part 4b advanced at the entrance port of an installation part opened in the plug insertion hole 1a from the top part of the housing 1.

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