A mobile communication system in which, when transmission is performed from a base station to a terminal device, a modulation scheme is designated, from among at least two modulation schemes with different modulation levels, on the basis of reception quality at the terminal to perform transmission from the base station. The system includes a base station transmitting at a first transmission power using a frequency designed for, in a channel allocation scheme of the system, not causing interference with an adjacent base station and using a first modulation scheme, and a second channel transmitting at a second transmission power lower than the first transmission power, and when the base station uses the second channel, a second modulation scheme having a lower modulation level than the first modulation scheme is designated, and communication is performed.