1. A BCH (Bose-Chaudhuri-Hocquenghem) decoder in which a folded multiplier is equipped, the BCH decoder comprising: a key equation solver including a plurality of multipliers; wherein the multiplier includes a plurality of calculation blocks configured to perform a calculation operation, and each of the calculation blocks repeatedly performs a calculation operation of a calculation stage for a plurality of calculation stages, outputs one output value on the basis of at least one input value in each calculation stage, and is connected to at least one another calculation block to transfer an output value of a current calculation stage as an input value of the at least one another calculation block in a next calculation stage.