The purpose of the invention is to develop an improved device for injecting pulsed steam into a human or animal vessel (e.g. veins), especially tributaries and perforating veins to treat them through thermofibrosis. The device of the invention includes a water pulse generator (2) that produces micro pulses of pressurized sterile water a hand piece (3) that transforms pulses of water coming from the generator (2) into pulses of steam an endoluminal catheter (4) with a tubular part (23) for delivering the steam into the vessel connection means (5) between the hand piece (3) and the endoluminal catheter (4) and a programmable central processing unit (cpu) to control the water pulse generator (2) and the hand piece (3). The main features of the device according to the invention are: the tubular part (23) has a length comprised between 1 and 30 mm and is made of a polymer the distal end of the endoluminal catheter has a terminal and central opening and possibly transversal holes to treat dilated veins. For smaller veins and those close to the skin, the water pulse generator and the hand piece are designed and controlled by the cpu, so that pulses of steam are made from pulses of water which volumes are comprised between 5 and 70 μl, and can be injected into the vessel at a controlled period comprised between one pulse/ 0.5 s and one pulse/ 2s and/or there are decompression means of the steam coming from the hand piece.The method for treating tributaries and perforating veins is another part of the invention.Linvention a pour but de pourvoir à un dispositif perfectionné pour injecter un flux pulsé dans un vaisseau dêtre humain ou danimal (par exemple des veines), en particulier des affluents, et perforer des veines pour les traiter par thermofibrose. Le dispositif de linvention comprend un générateur dimpulsion deau (2) qui produit des micro-impulsions deau stérile mise sous pression une pièce à main (3) qui transforme des impulsions deau provenant du générateur (2) en i
