Apparatus and continuous process for converting hydrocarbons in the presence of a granular catalyst including a metal from group VI a, VII a or VIII, deposited on a carrier, comprising passing a charge of hydrocarbons with hydrogen through a series of at least two vertical catalytic zones in which the catalyst bed moves progressively downwardly, withdrawing progressively the catalyst from the bottom of the last catalytic zone, and reintroducing the same, after regeneration, at the top of the first catalytic zone.