The present invention relates to a portable wireless terminal, and in particular, a portable wireless terminal such as a cellular phone, etc., and its security system that can reliably prevent, by remote control, improper use of the portable wireless terminal by a third party when it is lost or stolen. The portable wireless terminal that uploads backup data to a center by remote control from the center via a wireless network includes: a data access control section 1-1 that, in response to an instructions from the center, prohibits access to the backup data retained by a portable wireless terminal or deletes the backup data; an encryption section 1-5 that encrypts the backup data by using a public key notified from the center or a public key owned by the portable wireless terminal itself in response to instructions from the center; and a data transmission section 1-2 to 1-4 that transmits the backup data split into a plurality of data fragments on a plurality of communication paths to the center according to transmission priority of the backup data that is notified from the center or owned by the portable wireless terminal itself.