An electron beam shaping device suitable for a machine for intraoperative radiation therapy, IORT - "Intra Operative Radiation Therapy" - such that said machine comprises a mobile unit, provided with a linear accelerator having a radiating head of electrons, and an operation control panel, which are connected by cable to each other, such that said forming device includes a circular applicator, comprising a cylindrical tube and having a conduit through which the beam is transmitted of electrons, configured to be fixed to said radiant head and which includes a proximal element, which is fixed to said radiant head, and a distal element (3), configured to be placed in contact with the area to be irradiated, and which is fixed to said proximal element, the forming device being characterized in that it comprises: - a plate (1), which is detachably fixed to said distal element (3) and which is provided with a hole (2) in correspondence with the circular applicator duct, - at least two flat elements (10), such that each flat element (10) comprises two overlapping plates (11, 12), which are fixed to each other through first mechanical coupling means (13), and so that each flat element (10) is fixed to said plate (1) in a variable position, continuously, depending on the fixing position of said first mechanical coupling means (13) and second mechanical coupling means (14), - in such a way that at least two flat elements (10) are reciprocally arranged in such a way which are adjacent to each other, and each flat element (10) slides with respect to another adjacent flat element (10) through mechanical guiding and sliding means (12C, 12D), such that the reciprocal arrangement of said at minus two flat elements (10) is ajust able in order to define an opening (20) of area smaller than that of the duct section of said circular applicator, - so that said two overlapping plates (11, 12) are made of different materials, so that a first plate (11) is made of a first biocompatible and
