To provide a handlebar switch mounting method capable of mounting an additional handlebar switch on a handlebar while enhancing the operability of an additional operational switch when a new electrical unit is separately added to a vehicle, using an existing switch case as it is, and reducing the manufacturing cost.

In the switch case mounting method for mounting an additional switch case 1 provided with operational switches 1a, 1b for operating an electrical unit additionally provided on a two-wheeler in addition to an existing switch case 2 on a handlebar H of the two-wheeler, a mounting space T is formed opposing an outer peripheral surface of the handlebar H between a holding grip G which is fitted to a fore end Ha of the handlebar H and gripped by a driver and the existing switch case 2, and the additional switch case 1 is fixed to the mounting space T.