An interference objective lens includes: an objective lens system; a beam splitter which is placed between a measurement surface of a measuring object and a tip end of the objective lens, which diverges light emitted from the objective lens into a reference optical path and a measurement optical path, and which outputs combined wave in which reflection light passing through the reference optical path and reflection light passing through the measuring object are combined; a reference mirror which is placed in the reference optical path and which reflects, by the beam splitter, light diverged into the reference optical path; a mirror holding member which has a spherical surface-shaped outer surface, and which holds the reference mirror such that a reflection surface of the reference mirror passes through a center of a spherical surface; a support member which has a spherical surface-shaped inner surface having a diameter which is substantially equal to the outer surface of the mirror holding member, and which supports the outer surface of the mirror holding member by the inner surface; and a reference mirror adjusting mechanism which adjusts a position of the mirror holding member in the support member.