An interconnecting adapter for LC type optical connectors, the adapter comprising: fitting portions (A, B) suitable for LC type optical connector plugs respectively provided in both ends of a connector housing so that optical axes are aligned; a sleeve holder suitable for installing and retaining each of leading end portions of the LC type optical connector plugs inserted from the fitting portions (A, B) in both ends, the sleeve holder being arranged in an inner portion of the connector housing; a shutter plate which is diagonally arranged and closing at least one fitting portion of said connector housing; wherein said connector housing has in its inner side of a side wall a guide groove line and a guide protrusion suitable for inserting and guiding the LC type optical connector plug from its fitting portion; wherein the adapter further comprises: a leaf spring which energizes the shutter plate in a closing direction; the shutter plate and the leaf spring being arranged in said fitting portion; and said shutter plate being opened against a pressing force of the leaf spring by inserting the LC type optical connector plug from the fitting portion of said connector housing so as to fit into said sleeve holder; and wherein an inner side of a side wall of the connector housing is provided with an abutting surface suitable to lock the side surface of a movable portion of the shutter plate in the diagonal arrangement, characterized in that: the connector housing has in its inner side of a side wall, in addition a fan shaped planar recess portion which conforms to a swing portion of the shutter plate, a part of the guide groove line and a part of the guide protrusion are cut so as to form the fan shaped planar recess portion and to form the abutting surface. fitting portions (A, B) suitable for LC type optical connector plugs respectively provided in both ends of a connector housing so that optical axes are aligned; a sleeve holder suitable for installing and retaining each of leading end portions of the LC type optical connector plugs inserted from the fitting portions (A, B) in both ends, the sleeve holder being arranged in an inner portion of the connector housing; a shutter plate which is diagonally arranged and closing at least one fitting portion of said connector housing; wherein said connector housing has in its inner side of a side wall a guide groove line and a guide protrusion suitable for inserting and guiding the LC type optical connector plug from its fitting portion; wherein the adapter further comprises: a leaf spring which energizes the shutter plate in a closing direction; the shutter plate and the leaf spring being arranged in said fitting portion; and said shutter plate being opened against a pressing force of the leaf spring by inserting the LC type optical connector plug from the fitting portion of said connector housing so as to fit into said sleeve holder; and a leaf spring which energizes the shutter plate in a closing direction; the shutter plate and the leaf spring being arranged in said fitting portion; and said shutter plate being opened against a pressing force of the leaf spring by inserting the LC type optical connector plug from the fitting portion of said connector housing so as to fit into said sleeve holder; and wherein an inner side of a side wall of the connector housing is provided with an abutting surface suitable to lock the side surface of a movable portion of the shutter plate in the diagonal arrangement, characterized in that: the connector housing has in its inner side of a side wall, in addition a fan shaped planar recess portion which conforms to a swing portion of the shutter plate, a part of the guide groove line and a part of the guide protrusion are cut so as to form the fan shaped planar recess portion and to form the abutting surface. the connector housing has in its inner side of a side wall, in addition a fan shaped planar recess portion which conforms to a swing portion of the shutter plate, a part of the guide groove line and a part of the guide protrusion are cut so as to form the fan shaped planar recess portion and to form the abutting surface.