A quick release device includes a cam portion and a lever connected to the cam portion, a cooperation unit with which the cam portion is pivotably engaged, a rod having a first threaded section at a first end thereof and the threaded section extending through the cooperation unit and into the cam portion and threadedly connected with a pin which transversely extends through the cam portion, a second end of the rod including a second threaded section which extends through a biasing unit and is connected with an adjustment member in the biasing unit. The biasing unit pulls rod in a direction away from the operation member. The biasing unit is a tubular member which accommodates the spring and the adjustment member therein.