An OCD measurement equipment, including a tunable laser system, and a method of measuring the CD of patterns formed on a substrate. A light source optical system emits light which wavelength changes over time. A projector optical system projects the light emitted from the light source optical system on the substrate. A substrate support unit supports the substrate. An image relay optical system relays light reflected by the substrate. An image detection optical system detects the light relayed by the image relay optical system using a detector which detects the spatial distribution of the light.