Abstract: A mower with a power-transmission mechanism made up with an outer ring gear and an annular gear set inside the outer ring gear with the outer teeth meshed with inner teeth of the outer ring gear. Inner teeth of the annular gear are meshed with the teeth of a central gear installed inside the annular gear. The number of teeth of the three gears are slightly different, and the gears are arranged so that the outer ring gear and the central gear are on a same center axis with the annular gear off the center axis. By driving the annular gear, the outer ring gear and the central gear are rotated in the opposite direction. Accordingly, blade wheels mounted on these two gears are turned in the opposite direction, thus cutting the grass efficiently.