A cutting tool including a substrate composed of a silicon nitride-based sintered body and a coating layer. The coating layer includes first, second, third and fourth layers. The first layer is located on the surface of the substrate and is composed of TiN having an average crystalline width of 0.1 to 0.4 μm. The second layer is located on the first layer and composed of Al2O3 having an average crystalline width of 0.01 to 1.5 μm. The third layer is located on the second layer and is composed of TiN having an average crystalline width of 0.01 to 0.1 μm which is smaller than that of the first layer. The fourth layer is located on the third layer and is composed of Al2O3 having an average crystalline width of 0.01 to 1.5 μm.