The invention discloses an automatic building board cutting device which comprises a base plate, supporting plates, a top plate, a cutting base plate, a base, an air cylinder, a lifting plate, a containing groove, a screw, a swivel nut, a connecting block, a tool apron, a cutter, a sliding block, a sliding groove, a storage groove, a hinge shaft, an installing plate and a supporting column; a rotating shaft is further arranged in the base, threaded sections are arranged at the two ends of the rotating shaft, the threaded directions of the two threaded sections are opposite, and threaded sleeves are installed on the threaded sections. The automatic building board cutting device is simple and reasonable in structure and quick and convenient to use; the screw can be used for achieving adjustment of the horizontal positions of the tool apron and the cutter, no dead corners exist during cutting, arranged pressure springs and stopping blocks can well press boards to be cut, and cutting is guaranteed; walking wheel mechanisms capable of being contained in the base are convenient to adjust, the functions of movement and positioning of the base can be achieved, carrying of the cutting device is facilitated, and the automatic building board cutting device is suitable for use and popularization.