PURPOSE: To eliminate the manual input of a use staring time and a use ending time to a computer by writing a reading time to a record, which defines an identifying symbol as a key, when the identifying symbol to be written to an identifying slip is read.

CONSTITUTION: In a computer 4 to compute a charge based on a customer code which is read by a bar code reader 3, an internal clock 5 is provided to compute the use starting time and use ending time and a calculation program 6 is provided to determine a charge computing expression with time control. When a bar code written to an identifying slip 1 is read for the first time, the record to define the bar code as the key is registered to a file 8 and the reading time is written to the record. Further, when the bar code is read for the second time, the record to define the bar code as the key is retrieved from the file and the charge is calculated with the time control from the first reading time and second reading time. Thus, the use charge is calculated without inputting manually the use starting time and use ending time to the computer.