A sterilization apparatus for sterilizing target objects using a sterilizing agent comprising: a sterilization chamber; a concentration chamber provided with a heater for concentrating the sterilizing agent; a vaporization chamber for vaporizing the sterilizing agent concentrated in the concentration chamber, the vaporization chamber being provided between the concentration chamber and the sterilization chamber; a vacuum device for evacuating the sterilization chamber and the vaporization chamber; first transfer means for transferring a sterilizing agent to the concentration chamber; second transfer means (211, 214, 215) for transferring the sterilizing agent from the concentration chamber to the vaporization chamber; third transfer means for transferring the sterilizing agent from the vaporization chamber to the sterilization chamber; receiving means for receiving a selection by a user of one mode from a concentrated mode for executing sterilization by using a sterilizing agent concentrated in the concentration chamber and a non-concentrated mode for executing sterilization by using a sterilizing agent not concentrated in the concentration chamber via an operation unit; and control means for controlling the first transfer means for transferring the sterilizing agent to the concentration chamber and the second transfer means (211, 214, 215) for transferring the sterilizing agent from the concentration chamber to the vaporization chamber; wherein the control means is arranged to, in the case where a selection of the concentrated mode is received by the receiving means (102, S110, fig.3), control the first transfer means to transfer the sterilizing agent to the concentration chamber before the sterilization chamber and the vaporization chamber are depressurized to a predetermined air pressure by the vacuum device so that a process of concentrating the transferred sterilizing agent is conducted for a predetermined period of time in the concentration chamber and to control the second transfer means (211, 214, 215) to transfer the sterilizing agent concentrated in the concentration chamber to the vaporization chamber after the sterilization chamber and the vaporization chamber have been depressurized to the predetermined air pressure by the vacuum device, and in the case where a selection of the non-concentrated mode is received by the receiving means (102, S110, fig. 3) to control the first transfer means to transfer the sterilizing agent to the concentration chamber after the sterilization chamber and the vaporization chamber have been depressurized to the predetermined air pressure by the vacuum device and to control the second transfer means (211, 214, 215) to transfer the sterilizing agent in the concentration chamber to the vaporization chamber. a sterilization chamber; a concentration chamber provided with a heater for concentrating the sterilizing agent; a vaporization chamber for vaporizing the sterilizing agent concentrated in the concentration chamber, the vaporization chamber being provided between the concentration chamber and the sterilization chamber; a vacuum device for evacuating the sterilization chamber and the vaporization chamber; first transfer means for transferring a sterilizing agent to the concentration chamber; second transfer means (211, 214, 215) for transferring the sterilizing agent from the concentration chamber to the vaporization chamber; third transfer means for transferring the sterilizing agent from the vaporization chamber to the sterilization chamber; receiving means for receiving a selection by a user of one mode from a concentrated mode for executing sterilization by using a sterilizing agent concentrated in the concentration chamber and a non-concentrated mode for executing sterilization by using a sterilizing agent not concentrated in the concentration chamber via an operation unit; and control means for controlling the first transfer means for transferring the sterilizing agent to the concentration chamber and the second transfer means (211, 214, 215) for transferring the sterilizing agent from the concentration chamber to the vaporization chamber; wherein the control means is arranged to, in the case where a selection of the concentrated mode is received by the receiving means (102, S110, fig.3), control the first transfer means to transfer the sterilizing agent to the concentration chamber before the sterilization chamber and the vaporization chamber are depressurized to a predetermined air pressure by the vacuum device so that a process of concentrating the transferred sterilizing agent is conducted for a predetermined period of time in the concentration chamber and to control the second transfer means (211, 214, 215) to transfer the sterilizing agent concentrated in the concentration chamber to the vaporization chamber after the sterilization chamber and the vaporization chamber have been depressurized to the predetermined air pressure by the vacuum device, and in the case where a selection of the non-concentrated mode is received by the receiving means (102, S110, fig. 3) to control the first transfer means to transfer the sterilizing agent to the concentration chamber after the sterilization chamber and the vaporization chamber have been depressurized to the predetermined air pressure by the vacuum device and to control the second transfer means (211, 214, 215) to transfer the sterilizing agent in the concentration chamber to the vaporization chamber.