At least a ball escape hole (10) of a ball circulation passage (7) is formed of a molded body (12) and the molded body (12) is formed integrally with a block body (13) having high rigidity through an insert molding process, thereby eliminating a drilling working, possibly reducing assembling processes and reducing generation of noise. It is preferred that the molded body (12) is provided with an inner peripheral portion of a direction changing passage (11) integrally connected with the ball escape hole (10) and joined with both end surfaces of the block body (13). Furthermore, it is preferred that the molded body (12) is provided with a retainer (17) extending along a loaded ball passage (8) and integrally connected, at its both ends, with the inner peripheral portion of the direction changing passage (11), thereby providing a closed sectional shape surrounded by the ball escape hole portion (10), the direction changing portion (11) and the retainer portion (17). IMAGE
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