A seat (10), in which the lower end of a back joint link (26) is linked to a vehicle side turnably, with tilting of a back main frame (16) around a tilting center (16A) locked by a reclining mechanism (18), to lock the turning of a first link (22), a back sub frame (24) and the back joint link (26) and hence lock the operation of a back link mechanism (14). Therefore, supporting rigidity of a back side unit (12B) from the rear side by a back link mechanism (14) (a back suppressor (24)) can be enhanced to sufficiently hold a crew seated in the seat (10).