The invention discloses a simple air purifying device. The simple air purifying device consists of a filter cylinder, an absorption filter screen layer, an air supply pipe, a detecting device, an exhaust net port, a filter layer replacement port, an outer packing box, a sound and noise isolation foam plate, an air blower and an air sucking pipe. The simple air purifying device is characterized inthat the outer packing box is a closed body; the sound and noise isolation foam plate is arranged in the outer packing box; the filter cylinder is positioned in closed space surrounded by the sound and noise isolation foam plate; the detecting device is arranged above the filter cylinder; the filter layer replacement port is positioned at the right lower corner of the filter cylinder, and penetrates through the sound and noise isolation foam plate and the outer packing box; one end of the air supply pipe extends into the absorption filter screen layer in the filter cylinder, and the other endof the air supply pipe is connected with the wind blower; the wind blower is positioned in the sound and noise isolation foam plate; one end of the exhaust net port is mounted on the filter cylinder;and the other end of the exhaust net port penetrates through the sound and noise isolation foam plate and the outer packing box to extend indoors. The simple air purifying device is low in cost, highin purifying efficiency and flexible and convenient to use.