PURPOSE: To properly adjust a gap between rotors while controlling engagement status of the rotors, by shifting a housing of a radial bearing in axial direction of the rotors so that the distance between axes of the male and female rotors can be adjusted.

CONSTITUTION: A radial bearing 20 is supported by an adjust screw 60, whose inner peripheral surface 60a is a cylindrical surface coaxial with a rotor, whose outer peripheral surface 60b is a column-like shape having an axial center slant with respect to the rotor. An inclined ring 70 for moving the adjust piece 60 in axial direction of the rotor is engaged with an inclined screw part 70a of a cover 4. A part of a circumference of the ring 70 involves a screw part 70b having an axial center parallel to the axial center of the rotor, while the screw part 70b being engaged with an outer ring retainer 50. When the inclined ring 70 is rotated, the adjust piece 60 is shifted axially and the distance between axes of the rotors is decreased, whereby a bearing gap can be adjusted.