A decoder that receives, as input, probability information AMP/C_Ry_t. This probability information is obtained by dividing a channel value obtained by multiplication of received value y_t and a predetermined coefficient AMP by the first additive coefficient C_R for regulating the amplitude of the received value y_t and the probability information 1/C_AAPP_t obtained by multiplying the a priori probability information APP_t by the reciprocal of the second additive coefficient C_A for regulating the amplitude of the a priori probability information APP_t to a soft-output decoding circuit. The soft-output decoding circuit, which may be a large scale intergrated circuit, generates log soft-output C_II_t and/or external information 1/C_AEX_t using additive coefficients for regulating the amplitude of arithmetic operations in the inside of the soft-output decoding circuit.