A method for producing a fiber reinforced resin molded body comprising two or more resin integrated carbon fiber sheets that are stacked and unified, wherein each of the resin integrated carbon fiber sheets comprises a carbon fiber sheet comprising carbon fibers and at least one resin selected from the group consisting of thermoplastic resin and thermosetting resin, the carbon fiber sheet comprises a unidirectional long fiber group spread and arrayed in one direction, and multidirectional fibers (22; 22a, 22b), and the multidirectional fibers (22; 22a, 22b) cross the carbon fibers constituting the unidirectional long fiber group, the method comprising: forming each of the resin-integrated carbon fiber sheets by: spreading a carbon fiber filament group by passage through a plurality of rollers or bars while tensioning the carbon fiber filament group to generate the multidirectional fibers (22; 22a, 22b) from the carbon fiber filament group so that the multidirectional fibers (22; 22a, 22b) cross the carbon fibers constituting the unidirectional long-fiber group of the carbon fiber sheet; and applying resin powder comprising at least one resin selected from the group consisting of thermoplastic resin and thermosetting resin to the carbon fiber sheet, heat-melting the resin powder in a pressure-free state, and cooling it to form a semipreg as a resin-integrated carbon fiber sheet; and stacking two or more of the resin-integrated carbon fiber sheets and applying heat and pressure on the stack to form the fiber reinforced resin molded body, wherein the rollers or spreading bars vibrate in a width direction of the carbon filament fiber group or the rollers are fixed or rotated during the spreading of the carbon filament fiber group, and the tension of the carbon fiber filament group is 2.5 N or more per 15,000 carbon fiber filaments, in order that the carbon fiber sheet has a tensile strength in a longitudinal direction of 80% or more of a tensile strength of the carbon fiber filament group before spreading. each of the resin integrated carbon fiber sheets comprises a carbon fiber sheet comprising carbon fibers and at least one resin selected from the group consisting of thermoplastic resin and thermosetting resin, the carbon fiber sheet comprises a unidirectional long fiber group spread and arrayed in one direction, and multidirectional fibers (22; 22a, 22b), and the multidirectional fibers (22; 22a, 22b) cross the carbon fibers constituting the unidirectional long fiber group, forming each of the resin-integrated carbon fiber sheets by: spreading a carbon fiber filament group by passage through a plurality of rollers or bars while tensioning the carbon fiber filament group to generate the multidirectional fibers (22; 22a, 22b) from the carbon fiber filament group so that the multidirectional fibers (22; 22a, 22b) cross the carbon fibers constituting the unidirectional long-fiber group of the carbon fiber sheet; and applying resin powder comprising at least one resin selected from the group consisting of thermoplastic resin and thermosetting resin to the carbon fiber sheet, heat-melting the resin powder in a pressure-free state, and cooling it to form a semipreg as a resin-integrated carbon fiber sheet; and stacking two or more of the resin-integrated carbon fiber sheets and applying heat and pressure on the stack to form the fiber reinforced resin molded body, spreading a carbon fiber filament group by passage through a plurality of rollers or bars while tensioning the carbon fiber filament group to generate the multidirectional fibers (22; 22a, 22b) from the carbon fiber filament group so that the multidirectional fibers (22; 22a, 22b) cross the carbon fibers constituting the unidirectional long-fiber group of the carbon fiber sheet; and applying resin powder comprising at least one resin selected from the group consisting of thermoplastic resin and thermosetting resin to the carbon fiber sheet, heat-melting the resin powder in a pressure-free state, and cooling it to form a semipreg as a resin-integrated carbon fiber sheet; and stacking two or more of the resin-integrated carbon fiber sheets and applying heat and pressure on the stack to form the fiber reinforced resin molded body, wherein the rollers or spreading bars vibrate in a width direction of the carbon filament fiber group or the rollers are fixed or rotated during the spreading of the carbon filament fiber group, and the tension of the carbon fiber filament group is 2.5 N or more per 15,000 carbon fiber filaments, in order that the carbon fiber sheet has a tensile strength in a longitudinal direction of 80% or more of a tensile strength of the carbon fiber filament group before spreading.