PURPOSE: To make firm connection without using a key and processing and deforming a transmission shaft by inserting a pair of cone rings, engaging with the end part of a transmission shaft, in the conical trapezoid insertion hole of an outer casing, and tightening the cone rings so as to be neared in an axis direction with a tightening means.

CONSTITUTION: A cone ring insertion hole 6 and a tapered surface 8 are formed on each of both ends and the outer periphery of an outer casing 1 respectively, the external shape of a pair of corn rings 2 is made a conical trapezoid engaging with the hole 6, and the insertion holes 10 of transmission shafts 21 and 22 are drilledly provided on a shaft center part. Moreover bolt insertion holes 11 and expanding slots in the axis direction are provided in the outer periphery side of the ring 2, and the tapered surfaces 17 abutting the tapered surfaces 8 of the casing 1 are formed on the inner surfaces of caps 5. Consequently firm connection can be made without processing and deforming the shafts 21 and 22 by inserting the cone rings 2, in which the shafts 21 and 22 are inserted, into the casing 1, and tightening the caps 5 with screw bolts 3 and nuts 4 and 4a.