A voice-operated system comprising: a processing device; and a controller that communicates with the processing device, the processing device comprising: an operating panel to display an operation screen for instructing a process to be executed by the processing device, and receive an instruction from a user; and an executing unit to execute a process corresponding to a command received from the controller, the controller comprising: a command generator to generate the command for the processing device based on an input voice; and a transmitting unit to transmit the command to the processing device, wherein when the voice instructs the processing device to execute a first process, the command generator generates a first command for instructing the operating panel to display the operation screen for instructing execution of the first process, and when the voice instructs the processing device to execute a second process, the command generator generates a second command for instructing execution of the second process, wherein the controller further comprises a storage to store first data and second data, the first data associating an instruction keyword with an identification number of the operation screen corresponding to the instruction keyword, the second data associating a specific instruction keyword, among a plurality of the instruction keywords, with the second command for instructing execution of a process corresponding to the specific instruction keyword, when the instruction keyword included in the voice is not included in the second data but is included in the first data, the command generator generates the first command by referring to the first data, and when the instruction keyword included in the voice is included in the second data, the command generator generates the second command by referring to the second data, wherein the first data further associates the instruction keyword with information on a higher-level screen located at a higher-level hierarchy relative to the operation screen corresponding to the instruction keyword, and when a plurality of instruction keywords are included in the voice, the command generator generates the first command for instructing the operating panel to display the higher-level screen common to the plurality of instruction keywords. a processing device; and a controller that communicates with the processing device, the processing device comprising: an operating panel to display an operation screen for instructing a process to be executed by the processing device, and receive an instruction from a user; and an executing unit to execute a process corresponding to a command received from the controller, an operating panel to display an operation screen for instructing a process to be executed by the processing device, and receive an instruction from a user; and an executing unit to execute a process corresponding to a command received from the controller, the controller comprising: a command generator to generate the command for the processing device based on an input voice; and a transmitting unit to transmit the command to the processing device, wherein a command generator to generate the command for the processing device based on an input voice; and a transmitting unit to transmit the command to the processing device, wherein when the voice instructs the processing device to execute a first process, the command generator generates a first command for instructing the operating panel to display the operation screen for instructing execution of the first process, and when the voice instructs the processing device to execute a second process, the command generator generates a second command for instructing execution of the second process, wherein the controller further comprises a storage to store first data and second data, the first data associating an instruction keyword with an identification number of the operation screen corresponding to the instruction keyword, the second data associating a specific instruction keyword, among a plurality of the instruction keywords, with the second command for instructing execution of a process corresponding to the specific instruction keyword, the first data associating an instruction keyword with an identification number of the operation screen corresponding to the instruction keyword, the second data associating a specific instruction keyword, among a plurality of the instruction keywords, with the second command for instructing execution of a process corresponding to the specific instruction keyword, when the instruction keyword included in the voice is not included in the second data but is included in the first data, the command generator generates the first command by referring to the first data, and when the instruction keyword included in the voice is included in the second data, the command generator generates the second command by referring to the second data, wherein the first data further associates the instruction keyword with information on a higher-level screen located at a higher-level hierarchy relative to the operation screen corresponding to the instruction keyword, and when a plurality of instruction keywords are included in the voice, the command generator generates the first command for instructing the operating panel to display the higher-level screen common to the plurality of instruction keywords.