A building block that can be assembled into structures without requiring special end or corner pieces. The output shaft is supportable by the housing in a first position relative to the input shaft in which the first and second axes are substantially parallel, and in a second position relative to the input shaft in which the first and second axes are non-parallel. A rotation difference calculator is configured to calculate a rotation difference between an input and an output of the at least one frictional engagement element. A time judgment unit judges whether or not a time difference from a time point when a measurement value obtained by the first movement sensor becomes a predetermined value or less to a time point when a measurement value obtained by the second movement sensor becomes the predetermined value or less is a first threshold value or more. At least one platform section includes a frame, a plurality of float arms movably coupled with the frame, an endless belt carried by the plurality of float arms, and a cutterbar assembly carried by the plurality of float arms and movable in a localized manner in upwards and downwards directions.