an air compressor includes a crankcase , a cylinder secured to the crankcase , a crankshaft disposed inside the crankcase and adapted to be rotated by a drive means , a piston reciprocatively installed inside the cylinder , and a connecting rod for connecting the crankshaft to the piston . part of the drive power circuit of the drive means is constructed so as to be cut off when displacement of the constituent members of the compressor other than predetermined displacement occurs and / or when the temperature inside the compressor rises above a predetermined value . thus the passage of electric current to the drive means is cut off , the compressor being brought to a halt without causing secondary damage to develop .