A production method of a preform for molding a fiber-reinforced resin beam comprising: (a) a reinforcing fiber base supply step for supplying a reinforcing fiber base (12, 13, 14, 15, 85, 95) comprising many reinforcing fibers, having therein matrix-resin-receiving spaces and being deposited with an adhesive resin on a surface thereof, to a position for processing, (b) a release sheet supply step for supplying a release sheet (12p, 13p, 14p, 52p, 53p, 54p, 71p, 142Ap, 142Bp, 142Cp, 142Dp, 211Bp) to said position for processing, (c) a release sheet lamination step for laminating said supplied release sheet (12p, 13p, 14p, 52p, 53p, 54p, 71p, 142Ap, 142Bp, 142Cp, 142Dp, 211Bp), at said position for processing, to at least a part of a surface of said supplied reinforcing fiber base (12, 13, 14, 15, 85, 95) along the lengthwise direction thereof, (d) a release sheet bonding step for bonding and integrating said release sheet (12p, 13p, 14p, 52p, 53p, 54p, 71p, 142Ap, 142Bp, 142Cp, 142Dp, 211Bp) to the surface of said reinforcing fiber base (12, 13, 14, 15, 85, 95), by said adhesive resin, by heating and pressing said reinforcing fiber base (12, 13, 14, 15, 85, 95) and said release sheet laminated on the surface of said reinforcing fiber base, and, (e) a shaping step for molding a preform for molding a fiber-reinforced resin beam having a cross-sectional shape comprising at least one linear portion and at least one bent portion connected to said linear portion, by heating and/or pressing, by using a shaping mold, said reinforcing fiber base (12, 13, 14, 15, 85, 95) to which said release sheet (12p, 13p, 14p, 52p, 53p, 54p, 71p, 142Ap, 142Bp, 142Cp, 142Dp, 211Bp) is bonded and integrated, characterized in that said reinforcing fiber base (12, 13, 14, 15, 85, 95) in said reinforcing fiber base supply step is a continuous reinforcing fiber base sheet, said reinforcing fiber base supply step is an intermittent reinforcing fiber base sheet supply step comprising a supply time zone in which said continuous reinforcing fiber base sheet is continuously supplied up to a predetermined length to be processed at said position for processing and a non-supply time zone in which said supply is stopped after said predetermined length is supplied, said release sheet (12p, 13p, 14p, 52p, 53p, 54p, 71p, 142Ap, 142Bp, 142Cp, 142Dp, 211Bp) in said release sheet supply step is a continuous release sheet, said release sheet supply step is an intermittent release sheet supply step comprising a supply time zone in which said continuous release sheet is continuously supplied up to a predetermined length to be processed at said position for processing and a non-supply time zone in which said supply is stopped after said predetermined length is supplied, wherein said supply of the reinforcing fiber base sheet (12, 13, 14, 15, 85, 95) in said intermittent reinforcing fiber base sheet supply step and said supply of the release sheet (12p, 13p, 14p, 52p, 53p, 54p, 71p, 142Ap, 142Bp, 142Cp, 142Dp, 211Bp) in said intermittent release sheet supply step are carried out intermittently at least two times, and synchronously with each other. (a) a reinforcing fiber base supply step for supplying a reinforcing fiber base (12, 13, 14, 15, 85, 95) comprising many reinforcing fibers, having therein matrix-resin-receiving spaces and being deposited with an adhesive resin on a surface thereof, to a position for processing, (b) a release sheet supply step for supplying a release sheet (12p, 13p, 14p, 52p, 53p, 54p, 71p, 142Ap, 142Bp, 142Cp, 142Dp, 211Bp) to said position for processing, (c) a release sheet lamination step for laminating said supplied release sheet (12p, 13p, 14p, 52p, 53p, 54p, 71p, 142Ap, 142Bp, 142Cp, 142Dp, 211Bp), at said position for processing, to at least a part of a surface of said supplied reinforcing fiber base (12, 13, 14, 15, 85, 95) along the lengthwise direction thereof, (d) a release sheet bonding step for bonding and integrating said release sheet (12p, 13p, 14p, 52p, 53p, 54p, 71p, 142Ap, 142Bp, 142Cp, 142Dp, 211Bp) to the surface of said reinforcing fiber base (12, 13, 14, 15, 85, 95), by said adhesive resin, by heating and pressing said reinforcing fiber base (12, 13, 14, 15, 85, 95) and said release sheet laminated on the surface of said reinforcing fiber base, and, (e) a shaping step for molding a preform for molding a fiber-reinforced resin beam having a cross-sectional shape comprising at least one linear portion and at least one bent portion connected to said linear portion, by heating and/or pressing, by using a shaping mold, said reinforcing fiber base (12, 13, 14, 15, 85, 95) to which said release sheet (12p, 13p, 14p, 52p, 53p, 54p, 71p, 142Ap, 142Bp, 142Cp, 142Dp, 211Bp) is bonded and integrated,