A tag access control system capable of setting an appropriate parameter for controlling a reader/writer can be provided. The tag access control system includes a control portion that controls data communication between an IC tag and a reader/writer by sending a command to the reader/writer in accordance with a parameter and receiving an execution result; and a parameter adjustment portion that adjusts the parameter to an appropriate value. The parameter adjustment portion includes a parameter change portion that changes the parameter a plurality of times, a result storage portion that records execution results of commands based on a plurality of parameters that are changed and a calculation portion that calculates an appropriate parameter based on the execution results stored in the result storage portion.