A welded portion inspection apparatus for inspecting a welding state of a welded portion formed at the time when a plurality of workpieces (W1, W2) is welded, the welded portion inspection apparatus comprising: a radiation portion for radiating a welding laser beam along a welding locus set in the workpieces (W1, W2) so as to weld the workpieces (W1, W2), or an inspection laser beam along a scanning locus set in a molten pool of the workpieces (W1, W2) that are molten by the welding laser beam; a light-receiving portion for receiving a returned light beam including at least one of reflection light of the welding laser beam or the inspection laser beam radiated by the radiation portion, the reflection light being reflected from the molten pool of the workpieces (W1, W2), vapor light caused due to melting and evaporation of the workpieces (W1, W2), and thermal radiation light emitted from the molten pool of the workpieces (W1, W2); and an inspection portion for inspecting a welding state of the welded portion of the workpieces (W1, W2) based on an intensity change of the returned light beam received by the light-receiving portion at the time when the welding laser beam is radiated along the welding locus or at the time when the inspection laser beam is radiated along the scanning locus, characterized in that: the radiation portion is configured so as to radiate the welding laser beam or the inspection laser beam several times along the same welding locus (C11, C51); and the inspection portion is configured so as to inspect the welding state of the welded portion of the workpieces (W1, W2) based on a periodicity of the intensity change of the returned light beam at the time when the welding laser beam or the inspection laser beam is radiated along the same welding locus (C11, C51). a radiation portion for radiating a welding laser beam along a welding locus set in the workpieces (W1, W2) so as to weld the workpieces (W1, W2), or an inspection laser beam along a scanning locus set in a molten pool of the workpieces (W1, W2) that are molten by the welding laser beam; a light-receiving portion for receiving a returned light beam including at least one of reflection light of the welding laser beam or the inspection laser beam radiated by the radiation portion, the reflection light being reflected from the molten pool of the workpieces (W1, W2), vapor light caused due to melting and evaporation of the workpieces (W1, W2), and thermal radiation light emitted from the molten pool of the workpieces (W1, W2); and an inspection portion for inspecting a welding state of the welded portion of the workpieces (W1, W2) based on an intensity change of the returned light beam received by the light-receiving portion at the time when the welding laser beam is radiated along the welding locus or at the time when the inspection laser beam is radiated along the scanning locus, characterized in that: the radiation portion is configured so as to radiate the welding laser beam or the inspection laser beam several times along the same welding locus (C11, C51); and the inspection portion is configured so as to inspect the welding state of the welded portion of the workpieces (W1, W2) based on a periodicity of the intensity change of the returned light beam at the time when the welding laser beam or the inspection laser beam is radiated along the same welding locus (C11, C51). the radiation portion is configured so as to radiate the welding laser beam or the inspection laser beam several times along the same welding locus (C11, C51); and the inspection portion is configured so as to inspect the welding state of the welded portion of the workpieces (W1, W2) based on a periodicity of the intensity change of the returned light beam at the time when the welding laser beam or the inspection laser beam is radiated along the same welding locus (C11, C51).