To provide a temperature distribution measuring apparatus that improves accuracy of measuring a temperature distribution.

A temperature distribution measuring apparatus 1 includes: an image guide 10 for transmitting light of a workpiece W; a CCD camera 30 for imaging the light having transmitted the image guide 10 with a plurality of pixels 31 to generate a luminance signal A; a personal computer 40 that calculates a measurement temperature Tm for each pixel 31 by use of a conversion factor K with respect to a luminance value B obtained from the luminance signal A; and a monitor 50 for displaying the temperature distribution image of the workpiece W on the basis of the measurement temperature Tm. The image guide 10 has, in a longitudinally perpendicular cross section, a core part 14 arranged in a matrix and corresponding to each of the pixels 31 of the CCD camera 30. In a longitudinally perpendicular cross section of the image guide 10, the cross sectional area of an outer core part located radially outward from a shaft center O1 is larger than the cross sectional area of an inner core part located radially inward from the shaft center.