Provided are an optical device including a multilayer reflector having a layer whose optical thickness is not λ/4, and a vertical cavity surface emitting laser using the optical device. A resonance frequency shift or a reduction in reflectivity which is caused by a deviation from an optical thickness of λ/4 can be suppressed to improve characteristics and yield. The optical device for generating light of a wavelength λ includes a reflector and an active layer. The reflector is a semiconductor multilayer reflector including a first layer and a second layer which are alternatively laminated and have different refractive indices. The first layer has an optical thickness smaller than λ/4. The second layer has an optical thickness larger than λ/4. The interface between the first layer and the second layer is located at neither a node nor an antinode of an optical intensity distribution within the reflector.