A navigation device, comprising: an instruction receiving unit adapted to receive, from an external device (600, 700), a processing instruction containing an instruction ID; a processing unit adapted to perform processing according to the processing instruction received by the instruction receiving unit, the processing instruction including a parameter; an output unit adapted to output output information obtained as a result of the processing performed by the processing unit; a communication unit adapted to communicate with the external device (600, 700) through a communication network; wherein the instruction receiving unit is arranged: (i) to receive the processing instruction from the external device (600, 700) through the communication unit and the instruction receiving unit is further arranged, with reference to a command conversion table that stores relationships between received instruction IDs of processing instructions and corresponding execution commands thereby to allow mapping of received processing instructions to corresponding executable commands, (ii) to select a corresponding one of the execution commands that performs said processing as instructed by said received processing instruction; and the output unit is further arranged to send output information obtained as a result of the processing performed by the processing unit to the external device (600, 700) through the communication unit; and wherein operation of the navigation device is controlled remotely over the communication network by the external device (600, 700); and wherein the navigation device further includes: a state notification part adapted to monitor an operating state of the navigation device during remote control thereof, the state notification part further arranged to send an interrupt notification over the communication network to interrupt remote control of the navigation device in response to monitored operating state indicating that: (i) the navigation device is in a guidance mode at an intersection, or (ii) the navigation device is receiving input directly through a input receiving part of the navigation device. an instruction receiving unit adapted to receive, from an external device (600, 700), a processing instruction containing an instruction ID; a processing unit adapted to perform processing according to the processing instruction received by the instruction receiving unit, the processing instruction including a parameter; an output unit adapted to output output information obtained as a result of the processing performed by the processing unit; a communication unit adapted to communicate with the external device (600, 700) through a communication network; wherein the instruction receiving unit is arranged: (i) to receive the processing instruction from the external device (600, 700) through the communication unit and the instruction receiving unit is further arranged, with reference to a command conversion table that stores relationships between received instruction IDs of processing instructions and corresponding execution commands thereby to allow mapping of received processing instructions to corresponding executable commands, (ii) to select a corresponding one of the execution commands that performs said processing as instructed by said received processing instruction; and (i) to receive the processing instruction from the external device (600, 700) through the communication unit and the instruction receiving unit is further arranged, with reference to a command conversion table that stores relationships between received instruction IDs of processing instructions and corresponding execution commands thereby to allow mapping of received processing instructions to corresponding executable commands, (ii) to select a corresponding one of the execution commands that performs said processing as instructed by said received processing instruction; and the output unit is further arranged to send output information obtained as a result of the processing performed by the processing unit to the external device (600, 700) through the communication unit; and wherein operation of the navigation device is controlled remotely over the communication network by the external device (600, 700); and wherein the navigation device further includes: a state notification part adapted to monitor an operating state of the navigation device during remote control thereof, the state notification part further arranged to send an interrupt notification over the communication network to interrupt remote control of the navigation device in response to monitored operating state indicating that: (i) the navigation device is in a guidance mode at an intersection, or (ii) the navigation device is receiving input directly through a input receiving part of the navigation device. (i) the navigation device is in a guidance mode at an intersection, or (ii) the navigation device is receiving input directly through a input receiving part of the navigation device.