This invention relates to automatic locking alternating contact device in mechanic device, which comprises the following parts: left clamper, cover, direct current motor, clamper screw, upper cover, ringed dynamic probe, annealing isolation board, cover, drop head screw, right clamper board, stator, clamper screw, whorl bar and wheel, protruding axis, spring, fix screw, joint terminal, multilayer flexible conductive slice, insulation rack, drop screw bolt and fix bolt, insulation rack, slide wheels, bottom cover, protruding wheel, carbon brush, upper semi-round conductive electrode, inner ring and down semi-round electrode.