A node system comprising: an active system configured to execute processing; a standby system configured to perform at least one of scale-up and scale-down; and control means configured to instruct the standby system to perform the scale-up or scale-down, wherein the standby system, in performing the scale-up, is configured to increase number of virtual Central Processing Units, further referred to as virtual CPUs, included in the standby system and allocates one or more processes to one or more virtual CPUs added, while in performing the scale-down, the standby system is configured to decrease the number of virtual CPUs included in the standby system and releases allocation of one or more processes allocated to one or more virtual CPUs deleted, wherein the control means, upon reception of a completion notification of the scale-up or scale-down from the standby system, is configured to execute system switching to switch the standby system with the scale-up or scale-down thereof completed to a new active system and to switch the active system to a new standby system; wherein, when the active system needs to be scaled up, the control means is configured to instruct the standby system that completes the scale-up in response to a scale-up instruction from the control means, to switch to the new active system, after the system switching, the new standby system is configured to impose processing restriction that restricts an amount of call processing on the new active system, the control means is configured to instruct the new standby system to perform scale-up in the same way as the standby system that transitions to the new active system, and the control means, upon reception of a scale-up completion notification from the new standby system, is configure to release the processing restriction imposed on the new active system; and wherein, when the active system needs to be scaled down, the control means is configured to impose processing restriction that restricts an amount of call processing on the active system and then instructs the standby system to perform scale-down, the control means, upon reception of a scale-down completion notification from the standby system, is configured to issue an instruction of system switching, the control means, after the system switching, is configured to instruct the new standby system to perform scale-down in the same way as the standby system becoming the new active system, and the control means is configured to release processing restriction imposed on the new active system, upon reception of a scale-down completion notification from the new standby system. an active system configured to execute processing; a standby system configured to perform at least one of scale-up and scale-down; and control means configured to instruct the standby system to perform the scale-up or scale-down, wherein the standby system, in performing the scale-up, is configured to increase number of virtual Central Processing Units, further referred to as virtual CPUs, included in the standby system and allocates one or more processes to one or more virtual CPUs added, while in performing the scale-down, the standby system is configured to decrease the number of virtual CPUs included in the standby system and releases allocation of one or more processes allocated to one or more virtual CPUs deleted, wherein the control means, upon reception of a completion notification of the scale-up or scale-down from the standby system, is configured to execute system switching to switch the standby system with the scale-up or scale-down thereof completed to a new active system and to switch the active system to a new standby system; wherein, when the active system needs to be scaled up, the control means is configured to instruct the standby system that completes the scale-up in response to a scale-up instruction from the control means, to switch to the new active system, after the system switching, the new standby system is configured to impose processing restriction that restricts an amount of call processing on the new active system, the control means is configured to instruct the new standby system to perform scale-up in the same way as the standby system that transitions to the new active system, and the control means, upon reception of a scale-up completion notification from the new standby system, is configure to release the processing restriction imposed on the new active system; and wherein, when the active system needs to be scaled down, the control means is configured to impose processing restriction that restricts an amount of call processing on the active system and then instructs the standby system to perform scale-down, the control means, upon reception of a scale-down completion notification from the standby system, is configured to issue an instruction of system switching, the control means, after the system switching, is configured to instruct the new standby system to perform scale-down in the same way as the standby system becoming the new active system, and the control means is configured to release processing restriction imposed on the new active system, upon reception of a scale-down completion notification from the new standby system.