Abstract: Provided are an efficient quantum modular multiplier using characteristics of a modular operation, that is, a quantum modular multiplier having low quantum circuit complexity, and a quantum modular multiplication method. A quantum modular multiplier according to one embodiment of the present invention is a quantum modular multiplier for multiplying first qubits having N digits by second qubits having N digits (N is a natural number that is greater than or equal to 2) and includes a first auxiliary register setting unit, a second auxiliary register setting unit, an addition unit, and an auxiliary register initialization unit.