[en] Complete text of publication follows. With high-intensity RI beams provided by the RIKEN Accelerator Research Facility, various direct-reaction experiments have been performed at intermediate-energies in the reversed kinematics. Since the projectile-fragmentation scheme is used, the energy resolution of the separated RI beam is poor (a few %) and the intensity is low that favours a thick target. This makes the experiment quite difficult, especially in measuring the missing mass to separate nuclear levels in the final state. We adopt mainly two methods to overcome this difficulty: one is to measure the invariant mass and the other is the measurement of deexcitation γ rays. In the invariant mass method, particles decaying in flight is measured. The excitation energy of their parent nucleus is obtained from the invariant mass measured by their momentum vectors. The energy resolution is almost free from the energy spread of secondary beams, and is in the order of 100 keV for several tens A MeV incident energy. We have been studying, by this method, astrophysical (p,γ) processes with the Coulomb dissociation method. The processes ⁸B → ⁷Be+p, ⁹C → ⁸B+p, ¹²N → ¹¹C+p, ¹³O → ¹²N+p, ¹³N → ¹²C+p, and ¹⁴O → ¹³N+p were measured with Pb targets. Another application of the Coulomb dissociation is to measure the E1 strength function of very neutron-rich nuclei, such as ¹¹Li and ¹¹Be, where the 'soft mode' giant resonance is expected due to the neutron halo structure. The invariant mass method was applied also for the charge-exchange reaction. The isobaric analog states of ¹¹Li and ¹⁴Be in ¹¹Be and ¹⁴B, respectively, were excited by the (p,n) reaction in reverse kinematics. Their location was determined by measuring the three-body decay channels of the analog states. The mass of the particle-unbound nucleus ¹⁰He was determined also with the same method. The above Coulomb dissociation can be regarded as Coulomb excitation to continuum states. Usual Coulomb excitation to particle-bound states has also been studied for various unstable nuclei. Comparing the yield of deexcitation γ rays and theoretical prediction of the Coulomb excitation cross section, the transition probability of the relevant state can be extracted. We built an array of NaI(Tl) scintillators called DALI, and measured for the 2⁺-0⁺ transitions in ³²Mg, ³⁴Mg, ⁵⁶Ni, etc, and the E1 transition in ¹¹Be, ¹²Be and ¹⁵O. The same method was extended recently to (p,p') reaction and the (d,p) and (³He,α) transfer reactions. Properties of light neutron-rich nuclei is one of the major subject of research at RIKEN. In addition to the studies listed above, interaction cross section measurements, determination of neutron drip lines, and so on, have been extensively performed. (author)