The invention discloses a simple breathing device capable of rapidly replacing an oxygen cylinder for outpatient service of an oncology department. The simple breathing device comprises a bottom plate, wherein a fixing frame is arranged at a position, close to the edge of the right side, above the bottom plate, a fixing assembly is arranged at the left side of the fixing frame, the oxygen cylinder is arranged at the inner side of the fixing assembly, a connecting pipe is arranged above the oxygen cylinder, a pressure reducer is mounted at the top of the connecting pipe and located above the fixing frame, a winding assembly is arranged at the front side of the pressure reducer, a protective shell is arranged at a position, close to the upper right corner, above the fixing frame, and an oxygen mask is arranged in the protective shell. According to the simple breathing device, the connecting pipe is arranged, a first replacing opening and a second replacing opening can be connected with two oxygen cylinders at the same time through connecting hoses, when the oxygen cylinders are replaced, after the first replacing opening is connected with a new oxygen cylinder, and the old oxygen cylinder on the second replacing opening is detached, so that the original oxygen cylinder is prevented from being replaced after being detached, the oxygen cylinder is rapidly replaced, and the patient can normally inhale oxygen in an oxygen cylinder replacing process.