An analog input unit as an analog unit attached to a PLC includes an A/D converting unit as a first converting unit performing conversion between an analog value and a digital value according to a first conversion characteristic, a shared memory as a retaining unit retaining a conversion characteristic table indicating a second conversion characteristic of conversion between digital values, and a conversion processing unit as a second converting unit converting a digital value according to the second conversion characteristic by referring to the conversion characteristic table. The conversion characteristic table includes combinations of a first value that is a digital value and a second value that is a conversion result of the first value, the number of which corresponds to resolution of a digital value in the analog unit, and the second value of each of the combinations of the first value and the second value can be adjusted.