Communication terminal device, communication system, and communication method used by workers undertaking dangerous operations

A claimed communication terminal device comprising:

• a first communication unit, being a near-field communication unit, that communicates with a first communication terminal device using a near-field communication scheme;
• and
• an information storage medium that stores identifier mapping information that maps a first identifier identifying the first communication terminal device to a second identifier identifying a second communication terminal device, other than the claimed communication terminal device itself, that communicates by using a second communication scheme capable of communication over a longer distance than the first communication scheme;
• a control unit implemented at least by hardware resources whereby the control unit is configured to function as
• a searching unit that searches for the first communication terminal device via the first communication unit and acquires the first identifier of the first communication terminal device detected by the search, and
• a communication destination determination unit that acquires the second identifier mapped to the first identifier acquired by the searching unit, by referring to the identifier mapping information having been stored in the storage unit when the searching unit acquired the first identifier.