The origin band of the A (2)Pi<--X (2)Pi electronic transition of cyanotriacetylene cation has been detected in the gas phase. The ions were generated in a liquid-nitrogen cooled hollow cathode discharge incorporated in a multiple reflection cell. The technique of frequency modulation absorption spectroscopy is used to observe the band at Doppler-limited resolution. Analysis of the rotational structure yields accurate values of the rotational constants in the two electronic states, confirming a linear geometry. Comparison with astronomical measurements of diffuse interstellar bands is made.