The present invention relates to a mobile communication system and, more particularly, to a method for performing offline indication of a machine type communication (MTC) device in an MTC service. A network entity checks (or searches) whether or not an MTC device is out of monitoring or management because it is in an offline state. A network entity repeatedly transmits a signal for checking whether or not the UE is currently in an offline state to the UE during operation time of a timer, namely, during a detection time, or checks a signal (e.g., a message of an attach procedure, a message of a location registration procedure, and the like) transmitted by the UE during the detection time to check whether or not the UE is in an offline state. When the UE is checked to be in an offline state, the network entity informs an MTC server or an MTC user accordingly, to thus automatically manage a loss, malfunction, or the like, of the MTC device.