A microwave oven in which there is substantially no difference between time when a linearly traveling tray travels from the right side to the left side of a cooking chamber and time when the linearly traveling tray stays at the right side or the left side. The microwave oven includes a linearly traveling tray having a guide channel or hole guiding a linear movement and a power transmission transmitting driving power of a motor to the tray. The guide channel and the guide hole have an oval shape and adjust the staying time at the rightmost or leftmost side in the traveling region. A rotation tray having a locking step formed in the lower surface thereof is further provided. The power transmission may include a linkage, protrusion and/or a roller, and their modifications. Food is uniformly cooked at any place of the cooking chamber, and a user can easily clean and reinstall the tray.