In a steam cooker, for heating of a food which is a mass of granular matters or linear matters such as rice or chow mein, a steam superheater is not turned on or is turned on with a very weak electric power so that steam supplied from steam supply pipes (94A to 94C) is substantially not superheated. Steam of 80.degree. C. to 90.degree. C. derived from the steam supply pipe (94B) is jetted out right downward from an opening (111a) of a steam jet pipe (111). Then, steam located around an end portion of the steam jet pipe (111) in a tray-shaped case (51) is pulled in by steam jetted out from the opening (111a), so that a large amount of steam is jetted against a bowl of rice or a dish of chow mein. As a result, surfaces of, for example, rice grains are prevented from immediately going beyond 100.degree. C., so that condensation at the surfaces of the rice grains is efficiently achieved, and supply of condensed latent heat and penetration of condensed water (hot water) to the rice grains is efficiently achieved.