In a welded portion inspection device and a welded portion inspection method, an image of a welded portion including a reflection region of light is captured in a state where the light having a circular cross-sectional outer shape is projected on the welded portion. For the image, a circumscribed rectangle of the reflection region and an inscribed circle of the circumscribed rectangle are created. When the circularity of the inscribed circle is equal to or greater than a secondary determination threshold, the welding state of the welded portion is determined to be good.