We report translational diffusion coefficients in a columnar phase of a discotic liquid crystal formed by a triphenylene-based compound. The experiments were performed using ²H stimulated-echo-type pulsed-field-gradient spin-echo NMR applied to a chain-deutcrated sample. The diffusion coefficients were found in the range of 1× 10^-14-4 × 10^-14 m²/s, three orders of magnitude lower than in the isotopic phase of the same compound. This, together with the high activation energy obtained in columnar phase, indicates that the diffusion is dominated by solidlike jump processes.