The present invention has an object to provide an optical apparatus of VIPA-type for achieving the reduction of the inter-channel loss deviation to realize a high accurate demultiplexing function. To this end, the optical apparatus according to the present invention comprises: a collimator lens converting an input light into a parallel light; a phase mask changing a phase of the parallel light from the collimator lens to change the intensity distribution into a shape different from the Gaussian distribution; a line focal lens condensing the light output from the phase mask onto a one-dimensional direction; and a VIPA plate multi-reflecting the light condensed by the line focal lens to emit the multi-reflected light.