The present invention simply and clearly distinguishes shape retention such as anti-bending performance or anti-twisting performance of a tube that is the subject of comparison. One end (B1, C1) of a plurality of tubes (B, C) having the same length and different shape retention are attached to a first holding section (1), while at the same time the other ends thereof (B2, C2) are attached to a second holding section (2) in a manner so that the tube (B, C) bends at the same curvature. By means of moving one of the first holding section (1) or the second holding section (2) or relatively moving both the first holding section (1) and the second holding section (2) by means of a moving means (3), the tubes (B,C) are simultaneously further bent by the same amount in the direction of bending of each, and failure accompanying bending or twisting arises at some portion of the tubes (B, C).
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