There is provided a manufacturing method of a III-V compound crystal including a seed-crystal-formed substrate provision step of providing a seed-crystal-formed substrate in which a III-V compound seed crystal has been formed on a substrate, a seed crystal partial separation step of separating part of a portion in contact with the substrate in the III-V compound seed crystal from the substrate, and a crystal growth step of generating and growing the III-V compound crystal by reacting a group III element and a group V element with use of the III-V compound seed crystal as a nucleus after the seed crystal partial separation step.