A device for retaining the occupant of a vehicle seat during braking and / or impact, more particularly a retractable type of safety belt assembly, with four anchor points to the frame associated with a backrest extending between an upper and a lower part and a seat cushion extending between an inner and outer side and comprising in connected mode: a first portion of a retractable shoulder belt of which one end protrudes from a single belt retractor anchored to the vehicle frame, which extends from a first shoulder of the occupant and converges to the center of the lower abdomen; a second portion of a retractable shoulder belt of which one end protrudes from a single belt retractor anchored to the vehicle frame, which extends from the second shoulder of the occupant and converges to the center of the lower abdomen; a first portion of a retractable abdominal belt anchored to the vehicle frame, which extends horizontally from one of the occupant's hips to the center of the lower abdomen; a second portion of a retractable abdominal belt anchored to the vehicle frame, which extends horizontally from the other side of the occupant to the center of the lower abdomen; a closure system with a single buckle and a single tongue for the interconnection of the portions abdominal belts and portions shoulder belts; all the portions belts that converge at the center of the lower abdomen are joined by the closure system with the single buckle and the single tongue; it can adopt only two retractors,, installed to column mode, one on top of the other, or side by side fi space allows it, at the base, but not necessarily, of the vertical upright adjacent the seats, in slightly decentralized mode not to hinder the passage of the belt of the retractor placed lower to extend in height and containing each one, a single extractable independent belt wrapped in a single spool; the device is characterized by a reticular truss that has vertical and diagonal elements to its rails, for example of the type Hove or Prat or similar, installed between peaks of a right and left upright where the retractors are installed and whose diagonal and vertical elements are sufficiently distanced to allow the passage of the belts and of the integrated elements, anchor rings (29, 30) tongues and buckles, through the blanks of the reticular truss. a first portion of a retractable shoulder belt of which one end protrudes from a single belt retractor anchored to the vehicle frame, which extends from a first shoulder of the occupant and converges to the center of the lower abdomen; a second portion of a retractable shoulder belt of which one end protrudes from a single belt retractor anchored to the vehicle frame, which extends from the second shoulder of the occupant and converges to the center of the lower abdomen; a first portion of a retractable abdominal belt anchored to the vehicle frame, which extends horizontally from one of the occupant's hips to the center of the lower abdomen; a second portion of a retractable abdominal belt anchored to the vehicle frame, which extends horizontally from the other side of the occupant to the center of the lower abdomen; a closure system with a single buckle and a single tongue for the interconnection of the portions abdominal belts and portions shoulder belts; all the portions belts that converge at the center of the lower abdomen are joined by the closure system with the single buckle and the single tongue; it can adopt only two retractors,, installed to column mode, one on top of the other, or side by side fi space allows it, at the base, but not necessarily, of the vertical upright adjacent the seats, in slightly decentralized mode not to hinder the passage of the belt of the retractor placed lower to extend in height and containing each one, a single extractable independent belt wrapped in a single spool; the device is characterized by a reticular truss that has vertical and diagonal elements to its rails, for example of the type Hove or Prat or similar, installed between peaks of a right and left upright where the retractors are installed and whose diagonal and vertical elements are sufficiently distanced to allow the passage of the belts and of the integrated elements, anchor rings (29, 30) tongues and buckles, through the blanks of the reticular truss.