A height adjustment mechanism which, comprising - a control lever, - an input member driven with the first drive force by mentioned control lever, - a driving member where the motion given by said control lever is transmitted by mentioned input member, - drive bearings which act as bearing by compressing between said input member and driving member and which transmit the motion, - drive springs which hold mentioned drive bearings in their current positions, - brake bearings, - brake springs which allow mentioned brake bearings to be locked with pushing force, - a cover, - a single piece output member which is rotated as a result of motion incoming from said input member and so which moves the seat in desired directions, - a single piece base plate which receives the momentum incoming to mentioned output member and which allows bearings and springs to work within, - in order to allow the operating force and effort to be decreased by decreasing the friction between the brake bearings and mentioned base plate during rotation; at least one inclined and concave push surface which is formed on the mentioned driving member and pushes the brake bearings inwardly during rotation and - in order to allow the load to be received by driving member and the outer surface of the output member which are more durable, instead of bearings, for increasing the product life; a kinematic chain in which there is a direct contact between output member and drive surfaces of driving member when rotation momentum incoming from control lever disrupts braking by pressing onto brake bearings via said push surfaces of driving member adjusts the seat heights of both driver and passengers by allowing up and down motion of these seats and characterized in that mentioned input member which is the structure transmitting the motion given via control lever to driving member, stopping the driving member, and operating at a range of ±30°, comprises - input member-lock surfaces that compresses drive bearings with driving member-lock surface and transmits motion, - input member-positioning surfaces that is the angled surface which holds input member in its current position during first mounting and operation, - an input member-contact surface which contacts with driving member and decreases friction, - drive intervals that are the paths for the input member stopping elements on cover operate and restricts input member to operate in the range of ±30° by working together with input member stopping elements and - cover contact surfaces that decreases the contact between input member and cover and consequently decreases the friction. - a control lever, - an input member driven with the first drive force by mentioned control lever, - a driving member where the motion given by said control lever is transmitted by mentioned input member, - drive bearings which act as bearing by compressing between said input member and driving member and which transmit the motion, - drive springs which hold mentioned drive bearings in their current positions, - brake bearings, - brake springs which allow mentioned brake bearings to be locked with pushing force, - a cover, - a single piece output member which is rotated as a result of motion incoming from said input member and so which moves the seat in desired directions, - a single piece base plate which receives the momentum incoming to mentioned output member and which allows bearings and springs to work within, - in order to allow the operating force and effort to be decreased by decreasing the friction between the brake bearings and mentioned base plate during rotation; at least one inclined and concave push surface which is formed on the mentioned driving member and pushes the brake bearings inwardly during rotation and - in order to allow the load to be received by driving member and the outer surface of the output member which are more durable, instead of bearings, for increasing the product life; a kinematic chain in which there is a direct contact between output member and drive surfaces of driving member when rotation momentum incoming from control lever disrupts braking by pressing onto brake bearings via said push surfaces of driving member - input member-lock surfaces that compresses drive bearings with driving member-lock surface and transmits motion, - input member-positioning surfaces that is the angled surface which holds input member in its current position during first mounting and operation, - an input member-contact surface which contacts with driving member and decreases friction, - drive intervals that are the paths for the input member stopping elements on cover operate and restricts input member to operate in the range of ±30° by working together with input member stopping elements and - cover contact surfaces that decreases the contact between input member and cover and consequently decreases the friction.