An image-forming device includes an image-forming unit, a sensor, a calculating unit, and an extracting unit. The image-forming unit forms a plurality of marks on an object. The sensor detects a light reflected on the object, the reflected light including a plurality of waveforms. The calculating unit calculates a first value of each waveform in a predetermined evaluation index, a second value of a basic waveform corresponding to an ideal mark in the predetermined evaluation index, and a matching rate of each waveform with the basic waveform based on both each first value and the second value. The extracting unit extracts, from the plurality of waveforms, waveforms whose matching rates satisfy a predetermined condition.