With the advent of new radioactive isotope (RI) beam facilities
capable of producing intense beams of various nuclear species
far from stability, even at the drip-line, an increasingly large
amount of information on nuclear levels and modes of excitation
is being accumulated throughout the nuclear chart.

In this talk, I first mention RIKEN RI-Beam Factory (RIBF) with
its operation status. RIBF was proposed as a next generation of
facility for RI beam production, and came into operation recently.

Then I show results of two specific experiments at the existing
facility, in which an idea of applying (p,p') and (p,n) reactions
in inverse kinematics to structure studies of unstable nuclei
was successfully tested using the invariant mass method.
Finally, I would like to show a perspective to make these
measurements feasible at RIBF.