PURPOSE: To provide an automatic tooth brushing device that is especially able to automatically brush gaps among the whole teeth rapidly.

CONSTITUTION: When brushing teeth, a gear 8 is driven to move a plate 13b in the arrow (4) direction via a connecting bar 15, and width L of a brush body 2 is narrowed to be inserted into a mouth. For brushing teeth, a gear 7 is driven by driving a motor to vibrate a vibration transmission plate 9 at a specified period, resulting that a brush hair 4 implanted in the brush body 2 moves up and down within a specified length. This movement allows the teeth and gum that are in contact with the brush 4 to be brushed rapidly.