We can know many facts on solar flares by observing them with various instruments simultaneously. This figure shows the 1993-4-10 flare, which was observed by soft X-ray, hard X-ray, H-alpha line, photospheric magnetic field, and radio. These data indicate us that this flare was caused by an interaction between the large magnetic loop and the small loop (see panel d). (Reference: Hanaoka, Y., 1997, Solar Phys. 173, 319)