PURPOSE: To reduce loss, to raise compression efficiency and to improve workability at the time of manufacturing a blade by using a mold by optimizing the thickness of the blade in a backward impeller for a centrifugal compressor.

CONSTITUTION: The thickness of a blade in vertical direction and the thickness of the blade in circumferential direction in relation to the surface 20a of the blade in a cross-section perpendicular to the line of an axis 22 are determined so that inequalities r1<r2<r3, t1<t2<t3, h1<h2<h3 are satisfied, where (t) is the thickness of radius for the thickness of the blade in vertical direction, and (h) is the thickness of circumference for the thickness of the blade in the circumferential direction.