A massager includes a flexible outer housing, a driving housing, and an inclined expansion fastener. An upper end of the driving housing is cut into a plurality of elastic sheets. A cavity is defined at the upper end of the driving housing, and the inclined expansion fastener is partially disposed in the cavity. When the inclined expansion fastener moves downward, the inclined expansion fastener opens the plurality of the elastic sheets, so that a diameter of the upper end of the driving housing is increased; and when the inclined expansion fastener moves upward, the inclined expansion fastener moves out of the cavity at the upper end of the driving housing, the plurality of the elastic sheets rebound and reset, and the diameter of the upper end of the driving housing is restored.