Piston pin and method for manufacturing piston pin

A pin main body 10 is provided with a thinning hole 11 having: one-end-side and other-end-side large-diameter parts 11b, 11c provided to both longitudinal end sides of the piston main body; a central small-diameter part comprising a small-diameter part 11a and one-end-side and other-end-side medium-diameter parts 11d, 11e provided between the large-diameter parts; one-end-side and other-end-side first rounded parts 11f, 11h that are provided between the large-diameter parts and the central small-diameter part, the first rounded parts decreasing in inside diameter from the large-diameter-part sides toward the central-small-diameter-part sides, and the rate of change in inside diameter increasing from the large-diameter-part sides toward the central-small-diameter-part sides; and one-end-side and other-end-side second rounded parts 11g, 11i that are provided between the first rounded parts and the central small-diameter part, the second rounded parts decreasing in inside diameter from the first-rounded-part sides toward the central-small-diameter-part sides, and the rate of change in inside diameter decreasing from the first-rounded-part sides toward the central-small-diameter-part sides.