Disclosed is an apparatus for encoding k consecutive inputs indicating a TFCI (Transport Format Combination Indicator) of each of successively transmitted frames into a sequence of m symbols in an NB-TDD (Narrowband-Time Division Duplex) mobile communication system. An encoder encodes the k input bits into a sequence of at least 2.sup.n symbols where 2.sup.n>m, using an extended Reed-Muller code from a Kasami sequence. A puncturer performs puncturing on the sequence of 2.sup.n symbols from the encoder so as to output a sequence of m symbols.