To provide a public telephone system which is more user-friendly for mobile telephone users.

In the public telephone system comprising mobile telephones, each being integrated with a telephone directory function and with an infrared communication unit added thereto and public telephone sets, each with an infrared communication unit added thereto, each mobile phone side has a public phone utilizing mode, where a telephone number read by teleusing the telephone directory function is externally transmitted via the infrared ray communication unit based on the prescribed operation of a user and each public telephone set side is provided in addition with a function that makes automatic dialing to a telephone number, when receiving the telephone number from the mobile telephone via its infrared communication unit in a off hook state.