Abstract: The present invention provides a back exercise machine, which includes a support frame, a footrest, a protrusion device, and a grasping device. The support frame is disposed with a main post thereon. The footrest is mounted on a front end of the support frame. The protrusion device, which is composed of at least two struts pivotally interconnected with one another, is pivotally connected with the main post of the support frame for rendering a raising action and is installed with at least one elastic member between the struts for resiliently self-rebounding. The grasping device is mounted on the protrusion device for the user's two hands holding. In operation, the back exercise can raise the user's back to completely stretch the user's back extensor muscles so as to get rid of weariness by means of the protrusion device's struts pivoting with one another.