A slice management system that manages slices being virtual networks created on a network infrastructure, comprising: a Service Request Receiving unit configured to receive a service request containing service requirements wherein: functional requirements include mobility control, access area control and service use control, and performance requirements which include an allowed lower limit bandwidth, an allowed delay time and a minimum packet loss rate; an allocation determination unit configured to receive service requirements and slice information, use the service requirements and the slice information, and determine to which of an existing slice and a new slice the service is to be allocated; a resource utilization status information storage means configured to store information of a utilization status of resources allocated to created slices; a hardware utilization status information storage means configured to store information of a utilization status of hardware used for constructing the slice; and a resource change means (14, 35) configured to specify a slice based on the information of the resource utilization status stored in the resource utilization status information storage means and the information of the hardware utilization status information storage means in accordance with predication information of the resource utilization status by creation of the new slice or an extension of the existing slice, and reduce an amount of resources allocated to the existing slice when resources are found to be insufficient from the information of the resource utilization status and the prediction information. a Service Request Receiving unit configured to receive a service request containing service requirements wherein: functional requirements include mobility control, access area control and service use control, and performance requirements which include an allowed lower limit bandwidth, an allowed delay time and a minimum packet loss rate; functional requirements include mobility control, access area control and service use control, and performance requirements which include an allowed lower limit bandwidth, an allowed delay time and a minimum packet loss rate; an allocation determination unit configured to receive service requirements and slice information, use the service requirements and the slice information, and determine to which of an existing slice and a new slice the service is to be allocated; a resource utilization status information storage means configured to store information of a utilization status of resources allocated to created slices; a hardware utilization status information storage means configured to store information of a utilization status of hardware used for constructing the slice; and a resource change means (14, 35) configured to specify a slice based on the information of the resource utilization status stored in the resource utilization status information storage means and the information of the hardware utilization status information storage means in accordance with predication information of the resource utilization status by creation of the new slice or an extension of the existing slice, and reduce an amount of resources allocated to the existing slice when resources are found to be insufficient from the information of the resource utilization status and the prediction information.