A sphygmomanometer measures blood pressure in accordance with an oscillation in an artery wall, resulting from an arterial pulse correspondent with a change in cuff pressure. It comprises a cuff that is connected to the sphygmomanometer main body by a tube, a display unit for displaying the results of blood pressure measurements, and an air supply unit for supplying air to, and thus pressurizing, the cuff, which is detachable from the sphygmomanometer main body. The air supply unit is screwed into the sphygmomanometer main body with a screw assembly, and the screwed-in state is preserved by a caulking ring. The air supply unit also comprises a filter for keeping dust from entering the sphygmomanometer main body.