The present invention provides a femtosecond laser apparatus using laser diode optical pumping. To provide a stable mode locking and improve power stability and beam stability in an ultrafast laser such as a femtosecond laser, optical mounts which have mounted thereon optical parts of a diode pumping unit are mechanically engaged using bars of low thermal expansion coefficients and form a pumping module, and the pumping module is maximally separated from a laser platform or case.