A seat device in includes seat 2 and backrest 3 modules. The seat 2 includes a seat unit 21 with two frames 22 at its dies. The backrest module 3 comprises a back unit 31 with compensation units 4 located at its sides and connected with the supports 22. Two drivers 32 on the frames 22 control movement of the adjusters 4. Each adjustment unit includes a mount 41 pivoted to a rocker 42, which in turn can rotate about a lower portion 222 of one of the frames 22. The bracket 41 includes an indicating portion 411 proximate to the back of the seat 21 that moves from behind the seat 21 when the backrest 3 is upright to below the seat 21 when the back 3 is reclined. Link members 44 connect each mount 41 with the upper portion 221 of a corresponding frame. Driving units 32 are provided on the inner frames 22 for controlling the backrests 3.一種具有椅背傾斜補償之椅具，包含一個椅座裝置，及一個椅背裝置。該椅座裝置包括兩個左右間隔的內側架。該椅背裝置包括一個背靠單元，及兩個分別可調整角度地連接該背靠單元之左右兩側底部與該等內側架間的補償單元，每一個該補償單元具有一個連接該背靠單元的曲柄、一個可擺動地連接該曲柄之底部與相對應之該內側架的搖桿，及一個可擺動地連接該等曲柄之前側與相對應之該內側架的連桿。當該椅背裝置相對於該椅座裝置向後傾斜時，通過該等補償單元的連動補償，即會帶動該背靠單元向後且向下旋擺位移，並讓靠躺其上之使用者的背部及頭部，能夠服貼地隨著該背靠單元一起擺轉而不會相對滑動摩擦，故可符合人體工學設計。
