There are provided an inspection device and an inspection method for boiler furnace water wall tubes, which can inspect reduced wall thickness conditions of multiple water wall tubes, extending in an up-down direction along inner wall surfaces of a boiler furnace and arranged adjacent to each other, accurately and efficiently over a wide range based on surface shapes of the water wall tubes measured by a laser displacement sensor. A scanner 14 including columns 20 placed upright and fixed by magnets onto the surfaces of multiple water wall tubes 4 extending the up-down direction on the inner wall surfaces of the boiler furnace, a support frame 28 fixed to the columns 20 to support a displacement sensor 12 producing laser light to be irradiated onto the surface of a water wall tube 4, and a moving mechanism 31 for moving the displacement sensor 12 in the axial direction of the water wall tube 4 relative to the support frame 28. A signal processing unit 16 is also provided for calculating the amount of reduced wall thickness of the water wall tube 4 from a difference between the cross-sectional surface shape of the water wall tube 4 based on a signal from the displacement sensor 12 and a reference shape without reduction in wall thickness in order to evaluate a reduced wall thickness condition.