Provided is a silicon bulk thermoelectric conversion material in which thermoelectric performance is improved by reducing the thermal conductivity as compared with the prior art. In the silicon bulk thermoelectric conversion material, the ZT is greater than 0.2 at room temperature with the elemental silicon. In the silicon bulk thermoelectric conversion material, a plurality of silicon grains have an average of 1 nm or more and 300 nm or less, a first hole have an average of 1 nm or more and 30 nm or less present in the plurality of silicon grains and surfaces of the silicon grains, and a second hole have an average of 100 nm or more and 300 nm or less present between the plurality of silicon grains, wherein the aspect ratio of a crystalline silicon grain is less than 10.