A connection detecting mechanism of an optical connector plug comprising: a connector plug; a connection detecting device which is provided in a front face thereof comprising a light emission display portion for detecting connection and in a lower face further comprising a switch lever for detecting connection; and an optical adapter which is provided in both ends with fitting portions of the optical connector plug so that optical axes coincide with each other, for butt joining in an inner portion thereof ferrule leading end portions of the optical connector plug inserted from the fitting portions in both ends, wherein the switch lever in the lower face of the connection detecting device faces in a leading end thereof to a notch concave portion which is formed in an upper wall side of an opening end of the fitting portion in the optical adapter, wherein the switch lever is pushed up from a switch-off state to a switch-on state in which a lighting color of the on-state is displayed on the light emission display portion in the front face, when an optical connector plug is fully inserted to the fitting portion of the optical adapter instead of being in a half-inserted state, and wherein an optical adapter panel is provided in such a manner as to arrange side by side and mount a plurality of the optical adapters, an attaching recess having approximately the same width as a length of the connection detecting device is provided in the optical adapter panel in such a manner that the connection detecting device is arranged in an upper side of the optical adapter, and the light emission display portions in the front face of the connection detecting device are formed side by side in the upper and lower positions in correspondence to the fitting portions in both ends of each of the optical adapters. a connection detecting device which is provided in a front face thereof comprising a light emission display portion for detecting connection and in a lower face further comprising a switch lever for detecting connection; and an optical adapter which is provided in both ends with fitting portions of the optical connector plug so that optical axes coincide with each other, for butt joining in an inner portion thereof ferrule leading end portions of the optical connector plug inserted from the fitting portions in both ends, wherein the switch lever in the lower face of the connection detecting device faces in a leading end thereof to a notch concave portion which is formed in an upper wall side of an opening end of the fitting portion in the optical adapter, wherein the switch lever is pushed up from a switch-off state to a switch-on state in which a lighting color of the on-state is displayed on the light emission display portion in the front face, when an optical connector plug is fully inserted to the fitting portion of the optical adapter instead of being in a half-inserted state, and wherein an optical adapter panel is provided in such a manner as to arrange side by side and mount a plurality of the optical adapters, an attaching recess having approximately the same width as a length of the connection detecting device is provided in the optical adapter panel in such a manner that the connection detecting device is arranged in an upper side of the optical adapter, and the light emission display portions in the front face of the connection detecting device are formed side by side in the upper and lower positions in correspondence to the fitting portions in both ends of each of the optical adapters.