A driving force transmission mechanism includes a connection for integrally rotating a driving shaft on the driving source side and a driven shaft of a rotary member. The connection includes a tubular boss portion; and a fitting shaft portion fitted into the tubular boss portion. An inner shaft portion is provided in a projecting manner from bottom center of the tubular boss portion toward inside the tubular boss portion. An inner recessed portion into which the inner shaft portion fits is provided in center of a leading edge plane for fitting of the fitting shaft portion. Micro gaps are provided between an inner surface of the tubular boss portion and an outer surface of the fitting shaft portion and between an inner surface of the inner recessed portion and an outer surface of the inner shaft portion.