A data writing device includes a roller configured to convey a label including a radio tag along a predetermined path, a reader/writer configured to wirelessly communicate with the radio tag, and a controller configured to control the roller to convey the label and control the reader/writer to acquire a plurality of radio wave intensities from the radio tag at different positions along the predetermined path as the label is conveyed, and determine one of the different positions along the predetermined path at which the radio wave intensities are equal to or greater than a threshold value as a writing position for the radio tag.