A drive mechanism include a movable element which has at least one bearing arm; a linear guide shaft for linearly guiding the movable element without rotating; a driving device driving the movable element linearly along the linear guide shaft; a driven member driven, by the driving device, in a direction parallel to the linear guide shaft; a first guide hole formed on the bearing arm; a second guide hole formed on the driven member, the first and second guide holes being identical in size and in cross sectional shape; a tubular bearing member fitted into the first and second guide holes, the linear guide shaft being fitted completely through the tubular bearing member to be freely slidable therein; and a retaining device formed on the tubular bearing member and the driven member to prevent the tubular bearing member from moving relative to the driven member.