Objects of the present invention are to provide a positive working
presensitized plate of a thermal type, which has damage resistance, and
which is handled easily in conventional operation, high in sensitivity and
excellent in press life when used as a lithographic printing plate, and to
provide a support for a lithographic printing plate, which is suitably
used for the same. The objects have been achieved by a support for a
lithographic printing plate obtained by performing graining treatment,
alkali etching treatment and anodizing treatment on an aluminum plate,
wherein a ratio of a real area of a surface thereof to an apparent area of
the surface set larger by 1.3 to 1.8 times, comprising a pit having an
average diameter of 0.3 to 1.0 .mu.m and a micro grained structure inside
on the surface, wherein a ratio of an apparent area of the pits to the
apparent area of the surface is 90% or more; and a presensitized plate
comprising the support for a lithographic printing plate and a
photosensitive layer that can become alkali-soluble by heating provided on
the support.
