To provide a data processor capable of improving operability.

An IC recorder 10 is driven by power supplied from a battery 52 or power supplied from a PC 60 through a USB terminal 44 and executes data processing in relation with the PC 60. An MCU 14 discriminates which is the current state, a USB connection state or a USB unconnected state at the start of power supply. In the USB connected state, a USB mass storage mode is validated. At the USB unconnected terminal, whether the USB terminal is connected to the PC 60 is discriminated again. In the USB unconnected state, microphone mode selecting operation or a microphone mode releasing operation is received by a key entry device 42. A microphone mode flag 12f is set/reset, in response to the operation described. When the state is shifted to the USB connection state, after the start of power supply, the state of the microphone mode flag 2f is discriminated, and the mode corresponding to the discriminated result is validated.