A reduced-pressure device includes a housing having recesses on sidewalls thereof, an air pressure storage unit and a compression unit. The air pressure storage unit is installed in the housing and comprises a pressure storage container, a piston assembly and a piston spring, and the compression unit is mounted on the piston assembly. The compression unit further includes a pressing element and a turntable. The pressing element is accommodatable in the recesses of the housing, and rotatable by the turntable in relative to the air pressure storage unit and the housing, and when the pressing element is pulled out of the recesses and rotated to a predetermined position to compress the piston assembly to produce a negative pressure in the pressure storage container, the pressing element can be rotated back to the original position to be accommodated in the recesses again after using.