A method for manufacture of a resin tray comprising: a step of preparing a base mold comprising a plane installation side; a step of selecting block molds that should be installed on the installation side according to a specification of a tray that should be molded, the block molds comprising a bottom that touches the installation side and a side composed of a shaping surface, the block molds consisting of a first type comprising an extended block of a linear shape and corner blocks, mutually connected to constitute a circular body on the installation side, and a second type installed on the installation side within the circular body; a step of forming the circular body on the installation side by connecting the block molds of the first type, and constituting a pinch-off part at a circular top part of the circular body, and a cavity on a medial region of the circular body of the installation side; a step of line arranging a plurality of block molds of the second type at prescribed intervals on an inner side of the circular body, the block molds of the second type having a plurality of concave parts on an upper surface, and inserted pieces are fixed to prescribed concave parts in the block molds; a step where a molding surface is composed of the upper surface of the block molds fixed to the base mold; a step of obtaining a thermoplastic resin sheet by passing, in a perpendicular downward direction, a cylindrical parison, in a molten state pushed out from an extrusion slit, between a pair of rollers arranged under the extrusion slit to make it flat; a step where the thermoplastic resin material in the molten state is arranged opposite to the cavity; and a step where the thermoplastic resin material is molded by pushing it against the cavity. a step of preparing a base mold comprising a plane installation side; a step of selecting block molds that should be installed on the installation side according to a specification of a tray that should be molded, the block molds comprising a bottom that touches the installation side and a side composed of a shaping surface, the block molds consisting of a first type comprising an extended block of a linear shape and corner blocks, mutually connected to constitute a circular body on the installation side, and a second type installed on the installation side within the circular body; a step of forming the circular body on the installation side by connecting the block molds of the first type, and constituting a pinch-off part at a circular top part of the circular body, and a cavity on a medial region of the circular body of the installation side; a step of line arranging a plurality of block molds of the second type at prescribed intervals on an inner side of the circular body, the block molds of the second type having a plurality of concave parts on an upper surface, and inserted pieces are fixed to prescribed concave parts in the block molds; a step where a molding surface is composed of the upper surface of the block molds fixed to the base mold; a step of obtaining a thermoplastic resin sheet by passing, in a perpendicular downward direction, a cylindrical parison, in a molten state pushed out from an extrusion slit, between a pair of rollers arranged under the extrusion slit to make it flat; a step where the thermoplastic resin material in the molten state is arranged opposite to the cavity; and a step where the thermoplastic resin material is molded by pushing it against the cavity.