Abstract: The present invention relates to an adjustable backrest device, the backrest is divided into an upper recliner and a lower recliner, the lower end of the lower recliner is fixed to the backside of the seat portion, and the upper recliner and lower recliner are each included a pivotal connected portion for coupling to each other; a plural number of positioning apertures are disposed at the lower recliner and a retractable positioner is located at a predetermined area of upper recliner, when the upper recliner is swung to a desired angle of reclining, the positioiner can insert to the corresponding positioning aperture, so that the upper recliner can be adjusted and positioned in the desired angle as required by the user, therefore, the different reclining angles can be provided for the needs of the user so as to allow the user to efficiently stretch and comfort its back while reclining against the backrest.

Abstract: An office chair having a resilience tilt-adjusted device of a backrest includes an upper and a lower casing put together to cover an elastic adjuster which can press one end of elastic members with difference forces. Another end of the elastic members leans against an axle rod which is disposed at the lower end of the backrest supporter. The two ends of the axle rod pass through the casing. The lower end of the backrest is pivotally connected to a predetermined area within the casing as a pivot for swinging. A positioning rod having a rack is passed through the center of the axle rod so as to insert the rack onto the guiding groove of the casing. A positioning piece is arranged upon the rack and can be controlled to move up and down for inserting its end into the rack. Therefore, when the positioning piece is inserted into or exited from the rack, the backrest supporter can be positioned in a desirable angle after tilting.