In a video communication performed by using an imaging unit and a video display device, a communication terminal acquires a video captured by the imaging unit, stores at least a part of the acquired video in a storing unit, and determines a video of a predetermined interval after a start of the video communication being currently in progress from the stored video, as a replacement video. The diffusion screen includes a screen frame configured to be removably attachable to the enclosure with at least one releasable fastener, and at least a diffusion layer substantially spanning the screen frame to cover the air outlet to provide unidirectional or laminar air flow from the air outlet. An optical signal is input to the \u03c0-phase shifted FBG.