To provide a millimeter-wave module fastening structure that prevents stress due to thermal expansion and stress concentration.

A pin part 20a of a block member 20 is inserted into a diameter 18a of a flange part 18 sufficiently securing a gap shown in a millimeter-wave module fastening structure M, and inserted into and fixed in a pin hole 2c provided to a fixation place 2. An irregular member 30 is put over the block member 20, and two screw members 40 are inserted into a diameter 30a of the irregular member 30 and a diameter 20c of the block member 20, and inserted into and fixed in a screw hole 2d of the fixation place 2. The screw members 40 is inserted into a diameter 18b of the flange part 18 of a module assy part 10, and inserted into and fixed in a screw hole 2b provided to the fixation place 2. In a structure like this, a millimeter-wave module 10 is fixed to a case part 1 by fastening a waveguide part 11 of the millimeter-wave module 10 and a waveguide part 3 of the case part 1 using the block member 20 and irregular member 30.