A modular multiplier and a modular multiplication method are provided. The modular multiplier includes: a first register which stores a previous accumulation value calculated at a previous cycle; a second register which stores a previous quotient calculated at the previous cycle; a quotient generator which generates a quotient using the stored previous accumulation value output from the first register; and an accumulator which receives an operand, a bit value of a multiplier, the stored previous accumulation value, and the stored previous quotient to calculate an accumulation value in a current cycle, wherein the calculated accumulation value is updated to the first register, and the generated quotient is updated to the second register.