A wireless device configured to transmit wirelessly a first signal transmitted from a field device and receive wirelessly a second signal to be transmitted to the field device, the wireless device comprising: an antenna module; and a signal processing module, wherein the antenna module comprises: an antenna; a circuit configured to receive the first signal transmitted via a cable from the signal processing module and configured to transmit wirelessly the first signal from the antenna, the circuit being configured to generate the second signal based on a wireless signal received by the antenna and configured to transmit the second signal via the cable to the signal processing module; a housing (21, 41) that stores the circuit to cover circumference of the circuit; an antenna casing (22, 42) which is disposed in an end of the housing (21, 41) or between both ends (E1, E2) of the housing (21, 41), the antenna casing (22, 42) storing the antenna to enable the antenna to transmit and receive wireless signals; and a first connector that is connected to the housing (21, 41), the first connector being configured to input and output signals which are transmitted and received by the circuit, the first connector being connected to the signal processing module, wherein the antenna module is disposed outside the field device, wherein the signal processing module is disposed outside the field device, and the signal processing module is connected to the field device and connected via the cable to the antenna module, wherein the signal processing module comprises a semiconductor chip which performs communication processing with the field device, communication processing with the antenna module via the cable, and conversion processing of a communication protocol, and a housing that stores the semiconductor chip, wherein the first connector is connected to one end of the cable, and wherein the signal processing module further comprises a second connector that is connected to another end of the cable. an antenna module; and a signal processing module, wherein the antenna module comprises: an antenna; a circuit configured to receive the first signal transmitted via a cable from the signal processing module and configured to transmit wirelessly the first signal from the antenna, the circuit being configured to generate the second signal based on a wireless signal received by the antenna and configured to transmit the second signal via the cable to the signal processing module; a housing (21, 41) that stores the circuit to cover circumference of the circuit; an antenna casing (22, 42) which is disposed in an end of the housing (21, 41) or between both ends (E1, E2) of the housing (21, 41), the antenna casing (22, 42) storing the antenna to enable the antenna to transmit and receive wireless signals; and a first connector that is connected to the housing (21, 41), the first connector being configured to input and output signals which are transmitted and received by the circuit, the first connector being connected to the signal processing module, wherein the antenna module is disposed outside the field device, wherein the signal processing module is disposed outside the field device, and the signal processing module is connected to the field device and connected via the cable to the antenna module, wherein the signal processing module comprises a semiconductor chip which performs communication processing with the field device, communication processing with the antenna module via the cable, and conversion processing of a communication protocol, and a housing that stores the semiconductor chip, wherein the first connector is connected to one end of the cable, and wherein the signal processing module further comprises a second connector that is connected to another end of the cable. an antenna; a circuit configured to receive the first signal transmitted via a cable from the signal processing module and configured to transmit wirelessly the first signal from the antenna, the circuit being configured to generate the second signal based on a wireless signal received by the antenna and configured to transmit the second signal via the cable to the signal processing module; a housing (21, 41) that stores the circuit to cover circumference of the circuit; an antenna casing (22, 42) which is disposed in an end of the housing (21, 41) or between both ends (E1, E2) of the housing (21, 41), the antenna casing (22, 42) storing the antenna to enable the antenna to transmit and receive wireless signals; and a first connector that is connected to the housing (21, 41), the first connector being configured to input and output signals which are transmitted and received by the circuit, the first connector being connected to the signal processing module, wherein the antenna module is disposed outside the field device, wherein the signal processing module is disposed outside the field device, and the signal processing module is connected to the field device and connected via the cable to the antenna module, wherein the signal processing module comprises a semiconductor chip which performs communication processing with the field device, communication processing with the antenna module via the cable, and conversion processing of a communication protocol, and a housing that stores the semiconductor chip, wherein the first connector is connected to one end of the cable, and wherein the signal processing module further comprises a second connector that is connected to another end of the cable.