Vehicle seat for a passenger comprising: - a seat back with a front face towards the passenger and a back face opposite the front face, and - a folding element, particularly a tray, towards the back face of the seat back, installed free to pivot relative to the seat back about a rotation axis, so that the folding element can be put into at least two predetermined angular positions, including a raised position in which the folding element is not used, - a device for locking the folding element in position, characterised in that this device comprises: - a fixed element, fixed to said vehicle seat back, - a rotating element, fixed to said folding element, installed free to rotate relative to said fixed element about the rotation axis and being at least partially inserted in the fixed element, said rotating element comprising at least a first locking structure, - a locking element, installed on said fixed element and that can be moved between a locking position in which it locks said rotating element in rotation from said fixed element by at least partial engagement of said locking element in said at least one first locking structure of said rotating element, and a release position in which it allows free rotation of said rotating element from said fixed element by release of said locking element in said at least one first locking structure of said rotating element. - a seat back with a front face towards the passenger and a back face opposite the front face, and - a folding element, particularly a tray, towards the back face of the seat back, installed free to pivot relative to the seat back about a rotation axis, so that the folding element can be put into at least two predetermined angular positions, including a raised position in which the folding element is not used, - a device for locking the folding element in position, characterised in that this device comprises: - a fixed element, fixed to said vehicle seat back, - a rotating element, fixed to said folding element, installed free to rotate relative to said fixed element about the rotation axis and being at least partially inserted in the fixed element, said rotating element comprising at least a first locking structure, - a locking element, installed on said fixed element and that can be moved between a locking position in which it locks said rotating element in rotation from said fixed element by at least partial engagement of said locking element in said at least one first locking structure of said rotating element, and a release position in which it allows free rotation of said rotating element from said fixed element by release of said locking element in said at least one first locking structure of said rotating element. - a fixed element, fixed to said vehicle seat back, - a rotating element, fixed to said folding element, installed free to rotate relative to said fixed element about the rotation axis and being at least partially inserted in the fixed element, said rotating element comprising at least a first locking structure, - a locking element, installed on said fixed element and that can be moved between a locking position in which it locks said rotating element in rotation from said fixed element by at least partial engagement of said locking element in said at least one first locking structure of said rotating element, and a release position in which it allows free rotation of said rotating element from said fixed element by release of said locking element in said at least one first locking structure of said rotating element.