To provide a method of evaluating integrity in a boiler pipe and accessory pipe capable of objectively evaluating the integrity without depending on the level difference between persons in charge.

In the method, when a measured thickness value T2 is smaller than a required minimum thickness value T1, a first required minimum thickness value T3 is calculated at the maximum available pressure and at a normal temperature under the condition, a second required minimum thickness value T4 is calculated at the maximum available pressure and at a normal pressure under the condition, and a stage where it is determined whether both the first and second required minimum thickness values T3 and T4 are smaller than the measured thickness value T2 is used as a determination element. When both the first and second required minimum thickness values T3 and T4 are smaller than the measured thickness value T2, it is evaluated that the integrity passes.