The bending test at ordinary temperature is very widely used as a commercial mechanical test of metals and alloys next to the tensile test. The present author has made an investigation on the course of deformation at different parts of the test piece during bending and also the effects of the dimensions of the test piece, bending radius and the distance between two supports upon the severity of the test. Among the conclusions arrived at, the princi pal ones are as follows:-(1). The bending angle, if it exceeds a certain vulne, gives no influence upon the degree of severity. (2). For forged stecl, the distance between supports gives an influence upon the degree of severity when the specified bending angle is relatively small such as 90° or less. (3). For test pieces having constant. thickness, the severity slightly increases with the breadth. (4). When the section of the test piece is always square and both the bending radus and the thickness are increased, their ratio being kept constant, the severity slightly increases. (5). The specification for bending test, which has hitherto been used extensively in our country, has been compared with that established recently by the Japan Engineering Standards Committee. In the case of forged steel, the latter specification is decidedly looser than the formen. For cast steel the latter is looser than the former for bending angles of 90° or less, while the severities of these two specifications are almost equal when the angle is 120°.