A non-contact displacement sensor includes a focus timing calculator that, calculates a measurement-side focus timing at which measurement light is focused on a surface of a measurable object, a first reference-side focus timing at which reference light is focused on a first reference surface, and a second reference-side focus timing at which the reference light is focused on a second reference surface; a characteristics calculator that calculates the refractive index characteristics of a liquid lens apparatus based on the first reference-side focus timing, the second reference-side focus timing, and an optical path length difference; and a position calculator that calculates a position of the measurable object based on the refractive index characteristics and a phase of the measurement-side focus timing relative to a period of a drive signal.