The invention performs uniform chemical reactions with high efficiency by action of microwave onto reaction targets placed within a flow path along a center axis of a waveguide for transmission of microwave. The microwave chemical reaction device includes a circular waveguide for transmission of TM or TE mode microwave or a square waveguide for transmission of TE mode microwave and a flow path shielded from a space within the waveguide by a bulkhead of low microwave loss and coaxially extending along the center axis of the waveguide. Reaction targets to be subjected to chemical reactions are accommodated in the flow path and the microwave acts on the reaction targets within the flow path.