An airfoil, a turbine and a gas turbine having enhanced cooling performance are provided. The airfoil including a leading edge and a trailing edge may include: a first cooling passage connected to the leading edge; a second cooling passage connected to the trailing edge; a third cooling passage formed between the first cooling passage and the second cooling passage; a shock tube installed in the first cooling passage and configured to form an auxiliary cooling passage between the shock tube and the leading edge, and to include a plurality of dispersion hole in the shock tube; and a flow guide member installed on the shock tube and configured to guide a flow of air that is drawn from the third cooling passage into the first cooling passage.