A flexible screw type height control device comprises a housing, a servomotor mounted in the housing, a driving gear which is rotated by the servomotor, a driven gear which is provided with a spiral groove at a central portion thereof and is tooth-engaged with the driving gear, a flexible screw member which passes axially through the spiral groove of the driven gear and moves linearly upward and downward by the servomotor, and a telescopic unit including a plurality of sliding members which are slidably coupled to each other and cooperate with the flexible screw member. The flexible screw member is a coil spring. A first sliding member is slidably disposed in the housing. One end of the flexible screw member is extended outside the housing, and the other end is fixed to a last sliding member. Each sliding member is formed as an open-ended pipe and a cross-sectional area of the sliding members decreases from the first sliding member to the last sliding member.