A manufacturing method for an optical integrated circuit including a spatial reflection type structure having a perpendicular end surface and an inclined surface formed in an optical waveguide layer. The manufacturing method includes the steps of applying a first photoresist to the upper surface of the optical waveguide layer, removing the first photoresist except a portion corresponding to the inclined surface, and heating the first preferred embodiment to a given temperature to melt the first photoresist at least partially and deform the first photoresist by surface tension, thereby forming a first mask having an inclined shape. The manufacturing method further includes the steps of applying a second photoresist to the upper surfaces of the optical waveguide layer and the first mask, removing the second photoresist at a portion ranging from a position corresponding to the perpendicular end surface to a position corresponding to the upper end of the inclined surface to form a second mask, and etching the first mask, the second mask, and the optical waveguide layer by RIE to thereby simultaneously form the perpendicular end surface and the inclined surface.