The paper proposes an efficient Monte Carlo (MC) algorithm for simulating "hardly-relaxing" systems, where multiple replicas with different temperatures are simultaneously simulated, and a virtual process exchanges configurations between these replicas. This exchange process is designed to help systems at low temperatures escape from local minima. The method is applied to the three-dimensional ±J Ising spin glass model, and it is found that the ergodicity time in this method is significantly smaller than that of the multicanonical method. The time correlation function follows an exponential decay, suggesting rapid relaxation through the exchange process even at low temperatures. The order parameter distribution $P(q)$ is shown to be symmetric, indicating equilibrium. The method is advantageous over simulated tempering as it does not require estimating weighting factors and can be applied to various models without modification. However, it may not work well for systems with first-order phase transitions due to the difficulty in exchanging replicas across transition temperatures.The paper proposes an efficient Monte Carlo (MC) algorithm for simulating "hardly-relaxing" systems, where multiple replicas with different temperatures are simultaneously simulated, and a virtual process exchanges configurations between these replicas. This exchange process is designed to help systems at low temperatures escape from local minima. The method is applied to the three-dimensional ±J Ising spin glass model, and it is found that the ergodicity time in this method is significantly smaller than that of the multicanonical method. The time correlation function follows an exponential decay, suggesting rapid relaxation through the exchange process even at low temperatures. The order parameter distribution $P(q)$ is shown to be symmetric, indicating equilibrium. The method is advantageous over simulated tempering as it does not require estimating weighting factors and can be applied to various models without modification. However, it may not work well for systems with first-order phase transitions due to the difficulty in exchanging replicas across transition temperatures.