To provide a work machine capable of automatically controlling a blade attitude to a reference attitude on the basis of the stroke amounts of a pair of lift cylinders, and a method for automatically controlling a blade of the work machine.

A bulldozer 100 includes: a vehicle body 10; a blade 50; a pair of lift cylinders 60; a pair of pitch/tilt cylinders 70; a pair of lift stroke sensors 63; and a control section 220. The control section 220 drives the pair of pitch/tilt cylinders 70 at the same speed from a state in which the stroke amounts of the pair of lift cylinders 60 agree with each other. The control section 220 stops a right pitch cylinder 71 and a left pitch/tilt cylinder 72 when a stroke difference ΔS becomes larger than a threshold TH1.