A molecular beam source suppresses a temperature fall at the opening of a crucible, to make a temperature distribution within the crucible uniform and to prevent the phenomenon of bumping of a source substance, whereby the quality of an evaporated film can be enhanced. The source includes a heater disposed around the crucible which is formed of straight parts and U-shaped end parts continuously repeated at equal intervals. The straight parts are arranged so as to extend in a vertical direction of the crucible and the U-shaped end parts are bent outwards at outer-peripheral positions of the opening of the crucible.