PURPOSE: To obtain a gage for bending deformation, which is easily datachable and attachable to a test piece without positional mis-alignment nor coming off from the due position, in an occasion of rupture flexibility test of three points bending test for steel material and so on.

CONSTITUTION: To a saddle type gage for bending deformation detection of a test piece, a saddle type supporting table 3 having built-in screws 4 with which the table 3 is fixed to the test piece, a deformation beams 5 which follows deformation of the test piece, and a gage 2 which detects strain of the deformation beam. Accordingly, accurate bending deformation of the test piece can be detected, and an amount of average deformation of the test piece on the whole can be directly and precisely measured, and furthermore the saddle type gage for bending deformation detection does not move out of and come off the due position, even though shocking load is applied to the device during the test.