A thread shape measuring apparatus, comprising: an illuminating unit configured to emit first parallel lights having an optical axis in a direction orthogonal to a cross section including a thread axis of a thread portion to illuminate the thread portion, and to emit second parallel lights having an optical axis in a direction forming an angle (θ) larger than a lead angle (γ) of the thread portion with respect to the direction orthogonal to the cross section to illuminate the thread portion; an image-capturing unit that has a visual axis parallel to the optical axis of the first parallel lights, includes a telecentric lens, has a focusing position matching the cross section, and is configured to detect, out of the first parallel lights and the second parallel lights emitted from the illuminating unit, the light that has not been blocked by the thread portion to capture an image of the detected light; and an arithmetic operation unit that is configured to arithmetically operate a thread shape of the thread portion based on a captured image captured by the image-capturing unit, wherein the arithmetic operation unit is further configured to perform image processing on a first captured image captured by detecting, out of the first parallel lights emitted from the illuminating unit, the light that has not been blocked by the thread portion, to thereby calculate a first outline (P11, P21) being a partial outline of the thread portion along an axial direction of the thread axis in the cross section, perform image processing on a second captured image captured by detecting, out of the second parallel lights emitted from the illuminating unit, the light that has not been blocked by the thread portion, to thereby calculate a second outline (P3, P4) being a partial outline of the thread portion along the axial direction of the thread axis in the cross section, and arithmetically operate the thread shape of the thread portion based on the first outline (P11, P21) and the second outline (P3, P4) that are calculated. an illuminating unit configured to emit first parallel lights having an optical axis in a direction orthogonal to a cross section including a thread axis of a thread portion to illuminate the thread portion, and to emit second parallel lights having an optical axis in a direction forming an angle (θ) larger than a lead angle (γ) of the thread portion with respect to the direction orthogonal to the cross section to illuminate the thread portion; an image-capturing unit that has a visual axis parallel to the optical axis of the first parallel lights, includes a telecentric lens, has a focusing position matching the cross section, and is configured to detect, out of the first parallel lights and the second parallel lights emitted from the illuminating unit, the light that has not been blocked by the thread portion to capture an image of the detected light; and an arithmetic operation unit that is configured to arithmetically operate a thread shape of the thread portion based on a captured image captured by the image-capturing unit, wherein the arithmetic operation unit is further configured to perform image processing on a first captured image captured by detecting, out of the first parallel lights emitted from the illuminating unit, the light that has not been blocked by the thread portion, to thereby calculate a first outline (P11, P21) being a partial outline of the thread portion along an axial direction of the thread axis in the cross section, perform image processing on a second captured image captured by detecting, out of the second parallel lights emitted from the illuminating unit, the light that has not been blocked by the thread portion, to thereby calculate a second outline (P3, P4) being a partial outline of the thread portion along the axial direction of the thread axis in the cross section, and arithmetically operate the thread shape of the thread portion based on the first outline (P11, P21) and the second outline (P3, P4) that are calculated.