Abstract: In a dot impact printer, printing heads impact on an inked ribbon so as to form a pattern of dots on a paper sheet. The more often printing is carried out, the looser the central portion of the inked ribbon becomes. A sensor disposed perpendicularly against a surface of the inked ribbon detects such a condition of the inked ribbon, emitting a signal. Receiving the signal, a control means finds the inked ribbon unusable, interrupting the printing operation, and knowing a timing to replace the inked ribbon. The control means operates an alarm to urge replacement of the inked ribbon. Therefore, the dot impact printer is prevented from performing the printing operation under unfavorable conditions.