The present invention relates to a multichannel optical path changing device that is constituted of resin optical waveguides and mirrors and that changes a direction of an optical path. This device has monolithically formed cores having a mirror therebetween and optical path directions changed, and has multichannel cores simultaneously formed under a condition that their positional relationship is maintained. This device can be produced by a first or second method. The first method comprises steps of forming a parallelepiped block on a substrate by a cladding resin; forming a film of a core layer to cover the block by a core resin; and simultaneously forming cores having an optical path direction rectangularly changed, by selectively etching the core layer and the block. The second method comprises steps of forming a film of a core layer on a substrate by a resin; and simultaneously forming a plurality of cores having an optical path rectangularly changed, by selectively etching the core layer, under a condition that their positional relationship is maintained.