Equatorial electromagnetic ELF emissions at a frequency range around the oxygen ion gyrofrequency were observed in the low altitude plasmasphere (L=1.5--2.5) during magnetic storms with high activity of the ring current by triaxial search coil and single component electric field instruments on board the Akebono satellite. We find that a particular type of the ELF emissions occur with a multi-band spectral structure around the local gyrofrequency (FO+) of the oxygen ion (O+) during the main phase of magnetic storm. Our finding includes the following: The multi-band emissions are localized in the morning sector and often consist of several spaced frequency bands closely related the local gyro-harmonics of oxygen ion (O+) with a fundamental frequency of FO+ or 2FO+. The frequency of each band is dependent on the local magnetic field variation along the satellite orbit and the spacing between the bands is almost equal to FO+ or 2FO+. It is suggested that emissions are generated by terrestrial oxygen ion composing the ring current area during the main phase of magnetic storm.