A process for fabricating diamond from a starting powder material containing carbon as the principal component, and said process comprising bringing said powder material under high pressure, wherein, said powder material containing carbon as the principal component is a powder material containing C.sub.60 and/or carbon microtubules as the principal component, andsaid powder material is brought under high pressure by applying a gradient pressure to the material, while the portion of the powder material to which maximum pressure is applied is irradiated by a laser beam optionally through a diamond window material. An apparatus for fabricating diamond is also described.