In assembly of a number of optical devices (optical waveguide devices) to fabricate an optical module, the fabrication method of the optical module comprising: filling a plurality of openings for device mounting, the openings being formed on a platform, with a transparent liquid material; putting an optical waveguide device into at least one of the plurality of openings; and carrying out an active alignment process with the intention that a fine adjustment (waveguide alignment) of the position of each optical device can be realized with ease.