To provide a linear movement device capable of a high reduction ratio without tooth skipping and without the anxiety that the life of a belt is shortened by unreasonable force applied due to the twist of the driving belt.

The device has the first and second driving pulleys 9a, 9b with different diameters respectively of the driving pulley 9 and the first and second idling pulleys 11a, 11b with different diameters respectively of the pulley 11 and also the first and second intermediate pulleys 10a, 10b with different diameters respectively of the pulley 10 at the middle of the device and be able to slide. Two (2) driving belts 12, 13 are bound around these pulleys and driving pulley 9, the idling pulley 11 and the intermediate pulleys 10 are rotated by driving motor and the slide base 22 is moved to right or left direction with the differential reduction corresponded with the difference of the outer diameter of pulleys 9a and 9b or pulleys 10a and 10b.