DescriptionSimulator of quantum circuits is developed for massively parallel classical computers, and it is tested on the K computer in RIKEN R-CCS up to 45 qubits. Two optimization techniques are proposed in order to improve performance of the simulator. The "page method" reduces unnecessary copies in each node. It is found that this method makes approximately 17% speed-up maximum. Initial permutation of qubits is also studied how it affects performance of the simulator. It is found that a simple permutation in ascending order of the number of operations for each qubit is sufficient in the case of simulations of quantum adder circuits.