In an electrodeless discharge lamp using microwave energy, an electrodeless discharge lamp using microwave energy includes a resonator having an opening portion at the side and forming a resonance region at which microwave energy is resonated, a magnetron having an antenna in order to output microwave energy, a coaxial wave guide installed to the other side of the resonator, transmitting microwave energy from the magnetron to the resonator and having an internal guide extended in the projecting direction of the antenna of the microwave generator, a bulb placed inside the resonator and having enclosed fluorescent materials generating lights by the microwave energy, and a mesh member installed to the opening portion of the resonator, preventing leakage of microwave energy and passing lights generated in the bulb. Accordingly, by reducing a size of a lamp, it can be easily applied to a low-output system required a compact construction such as a projection TV, etc.