A method and an apparatus for transmitting and receiving signals modulated with 256 Quadrature Amplitude Modulation for use in a mobile communication system are provided. Capacities of each of confidential data segments, necessary when reading each of confidential data segments from an external memory and an internal memory, are acquired as control data from a register. is from 0 to 1 g, and a surfactant, wherein the cationized hydroxypropyl cellulose has an anhydroglucose-derived main chain and has a degree of substitution with cationized ethyleneoxy group of from 0.