The invention relates to a monitoring device (20) of the position of an assembly containing nuclear fuel (4) in a housing of a storage basket (2). According to the invention, it comprises at least one mobile stop device (24, 26, 28) and a position indicator (30) suitable for being held at a stop by the mobile stop device in a first position indicating that the assembly occupies a first position, said mobile stop device being arranged so as to be able to be placed, by means of contact with the assembly located in a second position in its housing, in a position enabling it to release the position indicator devised to move automatically from the first position to a second position indicating that the assembly occupies the second position.