A hollow drive gear reduction mechanism includes a hollow wave generator, an annular flexible bearing, a flexible wheel, and a rigid wheel. The annular flexible bearing is disposed in and driven to rotate by an elliptical recess of the wave generator. The flexible wheel includes an inner toothed section and is inserted in the annular flexible bearing and has an outer surface abutted against an inner surface of the inner ring, and the flexible wheel is driven to rotate by the annular flexible bearing. The rigid wheel includes a plurality of outer teeth which are different in number from the inner teeth of the flexible wheel, the rigid wheel is inserted in the flexible wheel, and a part of the outer teeth are meshed with the inner teeth. The respective components are hollow structures, and a lateral aperture is formed on the hollow wave generator.