A Montgomery modular multiplication device and an embedded security chip. The Montgomery modular multiplication device includes a first Montgomery modular multiplication module, a power calculation module and a second Montgomery modular multiplication module. The first Montgomery modular multiplication module obtains a first operation result A according to two first preset parameters. The power calculation module obtains a second operation result B according to the first operation result A output by the first Montgomery modular multiplication module, the first preset parameters, the second preset parameter and a power calculation function. The first Montgomery modular multiplication module further obtains a Montgomery modular multiplication conversion coefficient according to the first operation result A and the second operation result B. The second Montgomery modular multiplication module obtains a final modular multiplication result according to a first input parameter NA, a second input parameter NB and the Montgomery modular multiplication conversion coefficient.