To predict a correction rated life at high accuracy. A life predicting device executes step S1, step S2, step S4 for inputting specification information including a basic dynamic rated load C and basic static rated load C.sub.0, step 5 for computing a dynamic equivalent load P based on the specification information. step S3 for setting a reliability factor a.sub.1, step S7 and step S8 for determining a contact ellipse area S, step S9 for inputting a foreign substance purchasing diameter d.sub.debris ("debris" means "foreign substance"), step 10 for determining a standardized foreign substance diameter (d.sub.debris/ S), step S11 for setting a life correction coefficient a.sub.xyz based on the standardized foreign substance diameter, and step S6 and step S12 for calculating a correction rated life L.sub.nm based on the reliability coefficient, the life correction coefficient, the basic dynamic rated load and the dynamic equivalent load and the like.