The present invention relates to an optical data recording/reproducing device wherein an optical system holding portion holding a movable optical system having a carriage and a seek unit, and an emitting/detecting system holding portion holding an emitting/detecting system having an optical pickup unit are formed on the same housing. A number of components are reduced, a strength of the holding portions is improved, and an optical axis of each of systems is regulated with referring to the same housing. Therefore, an accurate assembling can be realized.