To reduce danger of deterioration of data transfer efficiency caused by a remainder from not being able to divide out a maximum packet size in an OBEX layer of a receiving side by a service data unit of a sending side in object exchange using infrared communication of an IrDA specification.

A secondary station uses a nickname of a primary station acquired from a negotiation parameter as a key to retrieve an SDU value from an SDU data table, and if the SDU value of the nickname is found in the SDU table (Yes of step S23), a maximum packet size to be communicated to the primary station is calculated from the SDU value (step S24). If the SDU value of the nickname is not found (No of step S23), the maximum packet size to be communicated to the primary station is set at a default value (step S25), and an SDU value determined by SDU size statistics information is added in coordination with the nickname to update the SDU table (step S31).