To provide a mechanical structure simply and surely assembled, and easily changing a sensor position after assembly.

First fixing connections 66, 68 are provided in main connection regions 42, 44 of a first structural member 32, continuously formed at a location spaced from contact faces of main connection regions 50, 52 in which second fixing connections 76, 78 are provided, generate a pressing reaction force S having a force component KA in the contact direction 58 by contacting pressing elements 80, 82, and include pressing faces 70, 72 on which the main connection regions 42, 44, 50, 52 are mutually fixed by the pressing reaction force S. The second fixing connections 76, 78 are provided in the main connection regions 50, 52 of second structural members 34, 36 and include the adjustable pressing elements 80, 82 overlapping with the first fixing connections 66, 68 in the contact direction.