Abstract: An elongated support frame is provided including front and rear ends. The front end supports a seat portion therefrom for adjustable positioning therealong and the rear marginal portion of the seat portion swingably mounts the lower end of an inclined backrest portion therefrom for angular displacement about a horizontal axis extending transversely of the support frame. The upper end of an upstanding prop is pivotally anchored to the upper free swinging end of the backrest portion and anchor structure is mounted from the rear of the support frame for angular displacement relative thereto about a horizontal transverse axis. The anchor structure defines an upstanding sleeve through which the lower end of the prop is slidably received and the sleeve is spaced forward of the axis of rotation of the anchor structure relative to the frame.