A collapsible element (5;5a) for a locomotive of a railway vehicle; the collapsible element comprising: - an absorption structure extending along a substantially horizontal axis, plastically deformable to absorb energy, and having a rear end connectable to a support and a front end supporting an anti-climber plate; - a guide device comprising: a) a stem, which is fixed to a rear face of said anti-climber plate and extends along said axis inside said absorption structure; b) a plurality of front partitions, which are orthogonal to said axis, are axially spaced from one another, are fixed to said absorption structure and have, at the center, respective guide holes engaged in an axially sliding manner by said stem; c) a rear partition, which is orthogonal to said axis, is axially spaced from said front partitions, is housed in said absorption structure, is fixed to said absorption structure and has, at the center, a first hole coaxial with said guide holes along said axis; d) a rear guide means (28c,7), which is axially spaced from said rear partition, is fixed with respect to said absorption structure, has a second hole (34, 9) coaxial with said guide holes and with said first hole and is axially more spaced from said anti-climber plate than said rear partition; characterized in that the said guide device also comprises a guide tube, which is coaxial with the said stem and with said guide holes, engages said first and second (34,9) hole, and has an internal diameter substantially equal to that of said guide holes, in such a manner as to guide an axial retraction of said stem during a plastic deformation of said absorption structure; said guide tube being stably fixed to said rear partition, so as to be movable together with said rear partition, and being axially slidable in said second hole (34,9) during a part of said plastic deformation. - an absorption structure extending along a substantially horizontal axis, plastically deformable to absorb energy, and having a rear end connectable to a support and a front end supporting an anti-climber plate; - a guide device comprising: a) a stem, which is fixed to a rear face of said anti-climber plate and extends along said axis inside said absorption structure; b) a plurality of front partitions, which are orthogonal to said axis, are axially spaced from one another, are fixed to said absorption structure and have, at the center, respective guide holes engaged in an axially sliding manner by said stem; c) a rear partition, which is orthogonal to said axis, is axially spaced from said front partitions, is housed in said absorption structure, is fixed to said absorption structure and has, at the center, a first hole coaxial with said guide holes along said axis; d) a rear guide means (28c,7), which is axially spaced from said rear partition, is fixed with respect to said absorption structure, has a second hole (34, 9) coaxial with said guide holes and with said first hole and is axially more spaced from said anti-climber plate than said rear partition; characterized in that the said guide device also comprises a guide tube, which is coaxial with the said stem and with said guide holes, engages said first and second (34,9) hole, and has an internal diameter substantially equal to that of said guide holes, in such a manner as to guide an axial retraction of said stem during a plastic deformation of said absorption structure; said guide tube being stably fixed to said rear partition, so as to be movable together with said rear partition, and being axially slidable in said second hole (34,9) during a part of said plastic deformation. a) a stem, which is fixed to a rear face of said anti-climber plate and extends along said axis inside said absorption structure; b) a plurality of front partitions, which are orthogonal to said axis, are axially spaced from one another, are fixed to said absorption structure and have, at the center, respective guide holes engaged in an axially sliding manner by said stem; c) a rear partition, which is orthogonal to said axis, is axially spaced from said front partitions, is housed in said absorption structure, is fixed to said absorption structure and has, at the center, a first hole coaxial with said guide holes along said axis; d) a rear guide means (28c,7), which is axially spaced from said rear partition, is fixed with respect to said absorption structure, has a second hole (34, 9) coaxial with said guide holes and with said first hole and is axially more spaced from said anti-climber plate than said rear partition;