Stephan's Quintet (SQ, HCG92) is a well studied compact group of galaxies with a disturbed intergalactic medium (IGM). An “intruder” galaxy NGC 7318b is currently colliding with the IGM at a relative velocity of 1000 km s−1, causing a large-scale shock front. We observed SQ with the Far-Infrared Surveyor (FIS) aboard AKARI in four far-infrared (far-IR) bands at 65, 90, 140, and 160μm. The 160μm image clearly shows an additional peak of emission overlying structure extending in the North-South direction along the shock ridge seen in the 140μm band, and in H2 and X-ray emission. Whereas most of the far-IR emission in the shocked region is from cold dust (20 K), the [CII]158μm emission - whose luminosity is comparable to that of the warm H2 gas - can significantly contribute to the single peak emission in the 160μm band. We conclude that the [CII] line emission comes from the warm H2 gas in the shock. Our result represents the first detection of shock-excited [CII] line emission.