The installation for amusement park, comprises at least one vehicle designed in such a way as to be able to accommodate at least one passenger in at least one seat, associated with at least one retention device. The retention device comprises a pivoting bar mounted on a retention element intended to retain the passenger in the seat. The retention element features a complex spatial shape, of which the lower part, intended to come in contact with the passenger's thighs, comprises for this purpose two recesses forming a hollow corresponding approximately to the size of the passenger's thighs.