PURPOSE: To lessen the influence of an optical fiber and lens by a difference in wavelength and to exactly receive the light from the optical fiber.

CONSTITUTION: This rotary joint 10 for bidirectional communication is constituted by freely rotatably connecting a rotating body 14 having a cylindrical optical path part 14b and a static body 12 having a cylindrical optical path 12b via bearings 16L, 16R. An optical fiber 88 is fixed to the cylindrical optical path part 14b by directing its end face 88a toward the cylindrical optical path part 12b and the lens 22 for converting divergent light 18 to collimated beams 20 of light is fixed thereto. A light emitting element 34 which generates collimated beams 30 of light and makes these beams incident on the end face 88 is fixed to the cylindrical optical path part 12b and the lens 26 for converting the collimated beams 20 of beam to convergent light 24 is fixed thereto. A light receiving element 28 receiving the convergent light 24 is fixed thereto.