A seat drive device, wherein one of first and second operation restricting portions corresponding to one of first and second transmission members is movable within one of first and second notches corresponding to another of the first and second transmission members when the one of the first and second transmission members is rotated from an initial state where both of the first and second transmission members are not rotated, and the first and second operation restricting portions are arranged to interfere with each other when both of the first and second transmission members are simultaneously rotated.