The present invention relates to an electric toothbrush brushing in only an end direction of a tooth, to which applied is a kinetic property generated by coupling a support point location variable lever device to a crank device. The electric toothbrush comprises: a motor generating power； a power transmitting means transmitting the driving power of the motor； a toothbrush head coupled to the power transmitting means to be operated； and a body embedding the motor and the power transmitting means therein. The electric toothbrush comprises a forward/reverse motor selectively driven in forward/reverse directions, and the power transmitting means comprises a motion changing lever variably changing an action location of a support point of a rotation movement of the forward/reverse motor to reciprocate in the horizontal direction while moving in the vertical direction in a constant trajectory. The electric toothbrush couples a toothbrush stick having a toothbrush head to the power transmitting means reciprocating in the horizontal direction with the constant trajectory such that motions of the toothbrush head brush from a gum covering a dental root only to an end direction of a tooth. Herein, the forward/reverse motor (a DC motor having a typical modulating means formed by a gear integrated) couples a crank having a crank pin to a power transmitting shaft for transmitting power. The power transmitting means has a motion change lever of which one end is coupled to the crank pin to form a point of force, and which makes the support point changed to be coupled to a support pin having a fixed location, and allows the toothbrush stick to be integrally coupled to a point of action on an end of the other side such that the toothbrush stick reciprocates in the horizontal direction while moving in the vertical direction in a constant trajectory. The present invention provides all users from children to the elderly with use convenience for the users to effectively brush their teeth.
