Provided is a heat treatment container having a small size and capable of efficiently performing a heat treatment on a SiC substrate. A heat treatment container is a container for a heat treatment on a SiC substrate 40 under Si vapor pressure. The SiC substrate 40 is made of, at least in a surface thereof, single crystal SiC. The heat treatment container includes a container part 30 and a substrate holder 50. The container part 30 includes an internal space 33 in which Si vapor pressure is caused. The internal space 33 is partially open. The substrate holder 50 is able to support the SiC substrate 40. When the substrate holder 50 supports the SiC substrate 40, an open portion of the container part 30 is covered so that the internal space 33 is hermetically sealed.