An optical non-destructive inspection method of determining a joint state of a joint portion on a joint interface between a first member and a second member of a measurement target object on the basis of measurement point information acquired from a measurement point set on a surface of the first member by irradiating the measurement point with heating laser, or on the basis of heating laser information about the heating laser and the measurement point information, the first member and the second member being joined to each other on the joint interface or being joined to each other with a joint member interposed between the first member and the second member on the joint interface, the optical non-destructive inspection method comprising: a heating laser emission step of emitting the heating laser toward the measurement point to heat the measurement point; an information acquisition step of acquiring the measurement point information which includes an intensity of infrared light radiated from the measurement point, or an information acquisition step of acquiring the measurement point information which includes an intensity of infrared light radiated from the measurement point and the heating laser information which includes an intensity of the heating laser which is radiated toward the measurement point; and a joint state determination step (S65, S70, S80; S65A, S70A, S80A) of determining the joint state of the joint portion on the joint interface using acquisition-associated information based on the measurement point information, or the measurement point information and the heating laser information, acquired in the information acquisition step (S37; S150); characterized by a preliminary heating step (S31A to S33), which is performed before the heating laser emission step, of causing thermal distortion in the first member by irradiating the measurement point, or a preliminary heating range that includes the measurement point, or one or a plurality of preliminary heating points set in advance in the preliminary heating range, with preliminary heating laser adjusted to a thermal distortion generation intensity, which is a constant output intensity, and an irradiation time such that thermal distortion is caused in the first member without destroying the first member so as to suppress occurrence of fluctuations in the joint state, wherein causing thermal distortion means causing deformation in the first member such that it is not restored to its original shape even when the temperature is lowered. a heating laser emission step of emitting the heating laser toward the measurement point to heat the measurement point; an information acquisition step of acquiring the measurement point information which includes an intensity of infrared light radiated from the measurement point, or an information acquisition step of acquiring the measurement point information which includes an intensity of infrared light radiated from the measurement point and the heating laser information which includes an intensity of the heating laser which is radiated toward the measurement point; and a joint state determination step (S65, S70, S80; S65A, S70A, S80A) of determining the joint state of the joint portion on the joint interface using acquisition-associated information based on the measurement point information, or the measurement point information and the heating laser information, acquired in the information acquisition step (S37; S150); characterized by a preliminary heating step (S31A to S33), which is performed before the heating laser emission step, of causing thermal distortion in the first member by irradiating the measurement point, or a preliminary heating range that includes the measurement point, or one or a plurality of preliminary heating points set in advance in the preliminary heating range, with preliminary heating laser adjusted to a thermal distortion generation intensity, which is a constant output intensity, and an irradiation time such that thermal distortion is caused in the first member without destroying the first member so as to suppress occurrence of fluctuations in the joint state, wherein causing thermal distortion means causing deformation in the first member such that it is not restored to its original shape even when the temperature is lowered.