The present invention provides a concave diffraction grating capable of improved diffraction efficiency by suppressing spherical aberration. The concave diffraction grating is a concave diffraction grating 2 for dispersing and focusing light and comprises sawtooth grating grooves 21 on a concave substrate 24, with the sawtooth grating grooves 21 being unequally spaced. The concave diffraction grating 2 for dispersing and focusing light is formed by preparing a planar diffraction grating with a sawtooth shape which is formed on a planar substrate by photo-lithography and etching or machining and which forms unequally spaced grating grooves 21, deforming and mounting the planar diffraction grating along a fixed convex substrate to obtain a mold of a concave diffraction grating, and transferring the mold of the concave diffraction grating to the surface of a metal or a resin.