To provide a gear case structure of a portable massage machine that can be easily formed by die-casting or resin molding and that can improve productivity.

The gear case 6 manufactured by die-casting or resin molding is made up of an upper case 6A into which bearings 13 rotatably supporting a pair of drive shafts 12 above a worm wheel 11 are assembled and an upper case 6B into which other bearings 13 rotatably supporting the drive shafts 12 below the worm wheel 11 are assembled. The bearings 13 assembled into the upper case 6A are stored and held in a bearing cover 17 fixed to the upper case 6A.