A battery pack production method is provided for producing a battery pack having several unit cells that are stacked with filling members interposed therebetween. The stacked unit cells are electrically connected. The battery pack production method includes measuring the thicknesses of the unit cells, arranging a filling member between adjacent ones the unit cells, and pressurizing the filling member to reduce a thickness of the filling member in the stacking-direction. In the battery pack production method, the thickness of the filling member is controlled based on the measured thicknesses of the unit cells after stacking according to at least one of: an amount of the elastic adhesives arranged; a length of time during which the elastic adhesives are pressurized; and a force pressurizing the elastic adhesives; and a distance between stacking-direction centers of two unit cells adjacent in the stacking direction is kept within a constant range.