  The J-PARC facility is near completion and experiments will start in 2009 on
nuclear and particle physics projects. In this article, the J-PARC facility is
introduced, and possible projects are discussed in high-energy hadron physics
by using the primary proton beam of 30-50 GeV. There are proposed experiments
on charm-production and Drell-Yan processes as well as single spin asymmetries
for investigating quark and gluon structure of the nucleon and nuclei.
Parton-energy loss could be studied in the Drell-Yan processes. There is also a
proposal on hadron-mass modifications in a nuclear medium by using the proton
beam. In addition, possible topics include transition from hadron to quark
degrees of freedom by elastic pp scattering, color transparency by (p,2p),
short-range correlation in nuclear force by (p,2pN), tensor structure functions
for spin-one hadrons, fragmentation functions, and generalized parton
distributions in the ERBL region although proposals are not written on these
projects. If proton-beam polarization is attained, it is possible to
investigate details of nucleon spin structure. In the last part of this
article, our own studies are explained on parton distribution functions in
connection with the J-PARC projects.
