A polishing apparatus with a film thickness measurement apparatus, the film thickness measurement apparatus is configured to measure the thickness of a film having a plurality of wiring patterns of a substrate during polishing of the film, wherein the polishing apparatus includes a polishing table for holding a polishing pad on which the film is pressed, and the polishing apparatus includes the film, the film thickness measurement apparatus comprises: a light emitter configured to project an emitted light during polishing of the film by the polishing apparatus; an optical condenser configured to condense the emitted light projected from the light emitter to provide a predetermined spot size and project the light onto the film while the film is pressed against the polishing pad; and a light receiver configured to receive a reflected light reflected from the film, and characterised in that an exposure time (t), which is a time during which the emitted light is projected to the film, is set so as to satisfy a following Formula: S + D × ω × t ≤ α × Smin where α is a value selected from a range of 0 < α ≤ 2, and where the spot size of the emitted light is D (μm), a spot area of the emitted light is S (μm 2), a peripheral velocity of the light emitter or the optical condenser during polishing of the film is ω (μm/sec), a minimum area as a minimum value of areas of respective wiring patterns constituting the plurality of wiring patterns is Smin (μm 2), and the exposure time is t (sec). the polishing apparatus includes a polishing table for holding a polishing pad on which the film is pressed, and the polishing apparatus includes the film, the film thickness measurement apparatus comprises: a light emitter configured to project an emitted light during polishing of the film by the polishing apparatus; an optical condenser configured to condense the emitted light projected from the light emitter to provide a predetermined spot size and project the light onto the film while the film is pressed against the polishing pad; and a light receiver configured to receive a reflected light reflected from the film, and characterised in that an exposure time (t), which is a time during which the emitted light is projected to the film, is set so as to satisfy a following Formula: S + D × ω × t ≤ α × Smin where α is a value selected from a range of 0 < α ≤ 2, and where the spot size of the emitted light is D (μm), a spot area of the emitted light is S (μm 2), a peripheral velocity of the light emitter or the optical condenser during polishing of the film is ω (μm/sec), a minimum area as a minimum value of areas of respective wiring patterns constituting the plurality of wiring patterns is Smin (μm 2), and the exposure time is t (sec). a light emitter configured to project an emitted light during polishing of the film by the polishing apparatus; an optical condenser configured to condense the emitted light projected from the light emitter to provide a predetermined spot size and project the light onto the film while the film is pressed against the polishing pad; and a light receiver configured to receive a reflected light reflected from the film, and characterised in that an exposure time (t), which is a time during which the emitted light is projected to the film, is set so as to satisfy a following Formula: S + D × ω × t ≤ α × Smin where α is a value selected from a range of 0 < α ≤ 2, and where the spot size of the emitted light is D (μm), a spot area of the emitted light is S (μm 2), a peripheral velocity of the light emitter or the optical condenser during polishing of the film is ω (μm/sec), a minimum area as a minimum value of areas of respective wiring patterns constituting the plurality of wiring patterns is Smin (μm 2), and the exposure time is t (sec).