To provide an apparatus for manufacturing a compound semiconductor single crystal by an LEC method, or the like in which the heat insulation of the outer periphery of a heater and the heat reflectance at the inner side surface of a structural member being a holding material are enhanced.

Heat reflection plates 10 to 12 made of PBN which is free from the degeneration even at high temperatures, does not cause adverse effects as an impurity on the properties of a growing crystal, and has a smooth surface and a color exhibiting a high heat reflectance or a pyrolytic carbon coat 9 which is free from the degeneration even at high temperatures, does not cause adverse effects as an impurity on the properties of the growing crystal and has a smooth surface, are provided on the inner side surface having a U-shaped cross section of the structural member 3 surrounding the heater 4 in a U-shape in its cross section from the outer peripheral side.