To provide a microwave plasma generation device and a microwave plasma generation method capable of stably and efficiently generating plasma.

In a microwave plasma generation device provided with a discharge tube 4 having a clad tube structure equipped with an outer tube 4a and an inner tube 4b, and a coaxial type microwave cavity 3a in which the discharge tube 4 is installed, the cross-sectional area of a space part between the outer tube 4a and the inner tube 4b is set constant. Use of an organic halogen compound decomposing microwave plasma generation device is effective for stabilizing plasma comprising a mixed gas of fluorocarbon or the like and steam. Because there is no tapered part nor a place where a passage is narrowed, the circulating wave effect is maintained, the melting of the discharge tube and the adhesion of solid substances can be prevented. An ignition coil or an ignition electrode is installed in the discharge tube, so that repeatable plasma generation can be executed regardless of a plasma state.