Abstract: A pivotable top board device for a chair includes an armrest having a coupling face with a first positioning hole. An axle block includes a first coupling face and a second coupling face. The first coupling face of the axle block is pivotably coupled to the coupling face of the armrest. The axle block further includes a through-hole extending from the first coupling face through the second coupling face. An operation rod longer than the through-hole is received in the through-hole and includes a first positioning end for disengagably engagement with the first positioning hole of the armrest and a second positioning end. The second coupling face of the axle block is pivotably coupled to a coupling face of a coupling board fixed to a top board. The coupling face of the coupling board includes a second positioning hole releasably receiving the second positioning end of the operation rod.