To enable estimation of a rolling life of a cam and roller and guarantee reliability of a cam follower.

This cam follower (rocker arm)1 is provided with a roller rolling on an outer circumference surface of a cam. When cam rolling life is defined as Lc, roller rolling life is defined as Lr, rolling life strength coefficient of cam material is defined as Bc, rolling life strength coefficient of roller material is defined as Br, safety factor is defined as f (provided, Lr/Lc>f>1), cam outer circumference length is defined as 1c and roller radius is defined as Rr, a relational expression 9 is satisfied, where m is 1/36 and n is 5/54.