Phase adjustment unit and valve timing changing device

This phase adjustment unit includes: a drive-side ring (22); a driven-side ring (31); multiple spherical bodies (40) that make contact with the drive-side ring with a first radius of rotation (R1), make contact with the driven-side ring with a second radius of rotation (R2) different from the first radius of rotation, and are pressed and sandwiched between the drive-side ring and the driven-side ring in at least the axial line direction (S); and an adjustment member (50) capable of adjusting the revolution of the multiple spherical bodies. Thus, it is possible to achieve a simpler structure, a reduction in the number of parts, a reduction in the size of the device, more flexibility in machining precision, and the like.