Since the discovery that microwave can heat metal powder, a number of studies on microwave heating of metal powder have been conducted. Because the microwave can heat various substances more efficiently than conventional heating, microwave heating of metal powder is highly expected to be applied in industry. In this paper, we design microwave heating apparatus for titanium powder for industrial mass production. The apparatus consists of some cavity resonators and a belt conveyor. Each resonator has additional two square openings other than microwave input for a belt conveyor, and they are set in parallel. Then we make the belt conveyor pass through the openings of the resonators and put the heated samples in cylindrical containers on the belt. In this condition, when the conveyor works, the samples are sent one after another, making it possible to heat metal powder seamlessly and efficiently. We evaluated this model by electromagnetic simulation, especially sample absorption and energy leakage from the openings, and investigated the optimal size for efficient heating. However in our simulations, because of the difficulty to simulate real titanium powder with complicated structure for limited computation resource, TiO2 bulk metal was applied as alternative of the titanium powder. The results show that the shorter vertical length of the openings gave more sample absorption, whilst horizontal length of the openings dis not affect sample absorption relatively. As for energy leakage from the openings, the shorter both vertical and horizontal length of the openings, the less energy leakage. Also paralleling resonators can reduce microwave leakage from the openings.