A fieldbus adapter connected between a fieldbus conforming to a foundation fieldbus, FF, standard specification and handling a digital signal and a field device handling an analog signal, the fieldbus adapter comprising: a first connection unit detachably connected to the fieldbus ; a second connection unit detachably connected to the field device ; a protocol stack conforming to one of FF H1 bus and HSE bus corresponding to the fieldbus ; a virtual field device object conforming to the foundation fieldbus standard specification, the virtual field device object including a function block application that includes an analog input block and an analog output block that are function blocks conforming to the foundation fieldbus standard specification; and an analog/digital conversion unit provided between the first connection unit and the second connection unit , the analog/digital conversion unit being configured to bidirectionally convert the digital signal handled by the fieldbus and the analog signal handled by the field device , wherein the analog/digital conversion unit is configured to read a primary value of the field device , which is an analog signal of 4 to 20 mA, and to convert the primary value into a digital value, the analog input block is configured to receive the digital value, and to output digital data that is a calculation result in the analog input block to the fieldbus via the protocol stack , the analog output block is configured to receive the digital data output from another field device or a manipulation monitoring apparatus to the fieldbus via the protocol stack , the analog/digital conversion unit is configured to convert a calculation result in the analog output block into an analog value and to output the analog value to the field device , and the field device is configured to receive the analog value. a first connection unit detachably connected to the fieldbus ; a second connection unit detachably connected to the field device ; a protocol stack conforming to one of FF H1 bus and HSE bus corresponding to the fieldbus ; a virtual field device object conforming to the foundation fieldbus standard specification, the virtual field device object including a function block application that includes an analog input block and an analog output block that are function blocks conforming to the foundation fieldbus standard specification; and an analog/digital conversion unit provided between the first connection unit and the second connection unit , the analog/digital conversion unit being configured to bidirectionally convert the digital signal handled by the fieldbus and the analog signal handled by the field device , wherein the analog/digital conversion unit is configured to read a primary value of the field device , which is an analog signal of 4 to 20 mA, and to convert the primary value into a digital value, the analog input block is configured to receive the digital value, and to output digital data that is a calculation result in the analog input block to the fieldbus via the protocol stack , the analog output block is configured to receive the digital data output from another field device or a manipulation monitoring apparatus to the fieldbus via the protocol stack , the analog/digital conversion unit is configured to convert a calculation result in the analog output block into an analog value and to output the analog value to the field device , and the field device is configured to receive the analog value. <EOS>