There is disclosed an operation input apparatus comprising a posture sensor attached to a finger, and a command generator for generating a command based on an output of the posture sensor. Each light source emits a light wave with a particular wavelength. The first echo canceller operates by first removing any persistent, non-echo signal that may be combined with the first echo signal, then training on the remaining, pure echo signal. The modular crypt structure may comprise a plurality of chambers, thereby providing a plurality of crypt modules, and the frame may comprise a plurality of horizontal bars and a plurality of vertical bars.