To lengthen a life and improve working accuracy in a throw-away type lathe turning tool for use mainly in lathe-turning a material hard to cut.

This throw-away type lathe-turning tool has the cutting edge angle αof a cross cutting blade 15a within a range of 5 to 25°, and a chip corner 14A interposed between the cross cutting blade 15a and a front cutting blade 15b is formed at an obtuse angle, whereby the damage of the cross cutting blade 15a and the chip corner 14a is suppressed to lengthen the life. In order to further lengthen the life of the chip corner 14A, preferably a sub-cutting blade formed on the corner 14A is formed in a circular-arc whose radius r1 of curvature ranges from 3 to 10 mm. Further, when a throw-away chip 10 is fixed to be pressed toward the base 2a and wall surfaces 2b, 2c of a chip seat, the movement of the throw-away chip 10 is prevented to suppress damage to the cutting blade and improve the working accuracy.