Abstract: A mobile device for filling at least one tube of a catalytic reactor consisting of a plurality of parallel tubes filled with a catalyst in a granular form. The device is characterised in that it includes: a catalyst storage trough with a sieve-type bottom, each hole of said bottom corresponding to a tube of the reactor; a catalyst dosing system for each tube to be filled; and means for the simultaneous release of the catalyst contained in the dosing system towards the at least one tube to be filled. The invention relates to a mobile device for filling at least one tube (1) of a catalytic reactor consisting of a plurality of parallel tubes (1) filled with a catalyst (9) in a granular form.