In accordance with one embodiment, a commodity sales data processing apparatus comprises a stationary type docking station with a storage module, and a portable information terminal which is attached to and detached from the docking station freely. The information terminal receives an input of data relating to the sales of a commodity to process the received data, and stores the data required to take over the processing in the storage module of the docking station Then the information terminal successively executes, if the information terminal is attached to the docking station, the processing by referring to the data stored in the storage module of the docking station.