There is provided a thermoelectric conversion material which is characterized by being composed of a sintered body of plate-like crystals of a composite oxide represented by general formula (2) BifCagM3hCoiM4jOk, and by having a density of 4.0-5.1 g/cm3. This thermoelectric conversion material is also characterized in that: when observed by SEM, the ratio of the plate-like crystals of a composite oxide represented by general formula (2) having an inclination in the major axis direction within 0±20° relative to the surface of the thermoelectric conversion material is 60% or more on the number basis; the average length of the lengths of the plate-like crystals of a composite oxide represented by general formula (2) is 20 μm or more; and the aspect ratio of the plate-like crystals of a composite oxide represented by general formula (2) is 20 or more.