An optical fiber device comprising a positioning/fixing substrate has a fiber guide and an optical fiber pressing spring formed in the fiber guide, and an optical fiber stored in the fiber guide. The optical fiber includes an end part having at least one marker groove. The fiber guide is a groove having two side wall surfaces. The optical fiber pressing spring includes a plate spring formed on one of the side wall surfaces in the fiber guide and an edge formed on the plate spring. The plate spring presses the edge to the side of the optical fiber with a fulcrum on one of the side wall surfaces, and the end part of the optical fiber is positioned by aligning the marker groove of the optical fiber with the edge of the optical fiber pressing spring.