The present invention relates to a seat cushion extension unit of the vehicle, is arranged slidably in a position protruding forward from the front end portion of the seat frame 110 of the vehicle and the extension portion 100, the seat frame in the locking position a the extension comprising a fixed and a release position, the locking device that slidably protrudes forward of the seat frame 200 and the lever 300 for controlling the locking device in the locked position and an unlocked position with respect to said extension member (100) It is supported by the housing (210) movably provided guide shaft 105 back and forth in the fixed to the seat frame 110 on both sides, the guide shaft is fixed in the housing 210 from the locked position of the locking device, release by being located in the configuration characterized in that to be able to move with respect to the seat frame, attached to the seat frame of the vehicle is improved usability can easily adjust to fit the body shape of the client, control the extension portion to move the spring friction on the guide shaft can be compared with the prior art there is a seat cushion extension structure for using the motor weight reduction and cost reduction are easy, and this with the effect that is not a noise, the seat cushion precise control effect.