To provide a straight movement device of a small size and a low cost which maintain a stable engaging condition of oscillation plates and a toothed rail.

In the straight movement device provided with toothed rail 40 forming plural teeth T1 projecting in the tooth height direction at a specific pitch in the longitudinal direction, plural fluctuation plates 53A having plural output teeth T2, a straight advance driving mechanism 50 having a case to house the input side and the driven side crankshafts 54 and 55 and the fluctuation plates 53A at the inside and to convert the input rotation into a relative movement of the case and the toothed rail 40, and a guide means to guide the case to the toothed rail 40 movable relatively, the crankshafts 54 and 55 at the input side and at the driven side are provided by extending in the tooth width direction of the toothed rail 40 respectively, in order to separate in the tooth height direction of the toothed rail 40 each other.