A mobile communication system, comprising: a radio terminal (UE 100) configured to perform a process of receiving a system information block from a base station (eNB 200) after an idle mode extended DRX is configured by a mobility management apparatus (MME 300C) to the radio terminal (UE 100), wherein, if the base station (eNB 200) supports an idle mode extended DRX, the system information block includes information indicating that the base station (eNB 200) supports the idle mode extended DRX, and if the base station (eNB 200) does not support the idle mode extended DRX, the radio terminal (UE 100) is configured to perform a process of stopping the operation of the idle mode extended DRX configured by the mobility management apparatus (MME 300C), wherein after configuring the idle mode extended DRX to the radio terminal (UE 100), the radio terminal (UE 100) is configured to determine a paging frame that is a radio frame including a paging occasion of the radio terminal (UE 100) and determine a predetermined subframe of the paging frame as the paging occasion, determine a paging hyper-frame that is a hyper-frame including the paging frame from a plurality of hyper-frames each including a predetermined number of radio frames, wherein the radio terminal (UE 100) is configured to determine the paging hyper-frame by using a third calculation formula defined separately of a first calculation formula used for determining the paging frame and a second calculation formula used for determining the paging occasion, and when a hyper-frame number of the paging hyper-frame is indicated by H-SFN, the number of hyper-frame corresponding to the extended DRX cycle is indicated by T eDRX' and a value based on a value unique to the radio terminal (UE 100) is indicated by α, the third calculation formula is H-SFN mod T eDRX = α mod T eDRX. a radio terminal (UE 100) configured to perform a process of receiving a system information block from a base station (eNB 200) after an idle mode extended DRX is configured by a mobility management apparatus (MME 300C) to the radio terminal (UE 100), wherein, if the base station (eNB 200) supports an idle mode extended DRX, the system information block includes information indicating that the base station (eNB 200) supports the idle mode extended DRX, and if the base station (eNB 200) does not support the idle mode extended DRX, the radio terminal (UE 100) is configured to perform a process of stopping the operation of the idle mode extended DRX configured by the mobility management apparatus (MME 300C), wherein after configuring the idle mode extended DRX to the radio terminal (UE 100), the radio terminal (UE 100) is configured to determine a paging frame that is a radio frame including a paging occasion of the radio terminal (UE 100) and determine a predetermined subframe of the paging frame as the paging occasion, determine a paging hyper-frame that is a hyper-frame including the paging frame from a plurality of hyper-frames each including a predetermined number of radio frames, wherein the radio terminal (UE 100) is configured to determine the paging hyper-frame by using a third calculation formula defined separately of a first calculation formula used for determining the paging frame and a second calculation formula used for determining the paging occasion, and determine a paging frame that is a radio frame including a paging occasion of the radio terminal (UE 100) and determine a predetermined subframe of the paging frame as the paging occasion, determine a paging hyper-frame that is a hyper-frame including the paging frame from a plurality of hyper-frames each including a predetermined number of radio frames, wherein the radio terminal (UE 100) is configured to determine the paging hyper-frame by using a third calculation formula defined separately of a first calculation formula used for determining the paging frame and a second calculation formula used for determining the paging occasion, and when a hyper-frame number of the paging hyper-frame is indicated by H-SFN, the number of hyper-frame corresponding to the extended DRX cycle is indicated by T eDRX' and a value based on a value unique to the radio terminal (UE 100) is indicated by α, the third calculation formula is H-SFN mod T eDRX = α mod T eDRX.