A method of manufacturing a lead frame with a mounted component, comprising: joining one metal plate having a plurality of terminals, a first connection portion that connects the plurality of terminals to each other, a first extension portion disposed on one end of the first connection portion to extend from the first connection portion in a first direction beyond the plurality of terminals, and a second extension portion disposed on the other end of the first connection portion 11 to extend from the first connection portion in a second direction opposite to the first direction and beyond the plurality of terminals, and another metal plate having an electronic component mounted thereon and having a first fitting portion comprising a pair of first clamping portions configured to clamp the first extension portion, and a second fitting portion comprising a pair of second clamping portions configured to clamp the second extension portion thereby joining the first and second metal plates (10, 50) together; and sealing the mounted component with a resin by using a mold, the mold comprising; a pair of first protrusion portions to press each portion of the pair of first clamping portions, respectively; and a pair of second protrusion portions to press each portion of the pair of second clamping portions respectively, wherein: in the step of sealing the mounted component with the resin, each portion of the pair of first clamping portions is pressed to be extended by the respective one of the pair of first protrusion portions, so that gaps between the first extension portion and the first clamping portions are filled, whereby the resin is prevented from leaking from between the first extension portion and the first clamping portions, and each portion of the pair of second clamping portions is pressed to be extended by the respective one of the pair of second protrusion portions, so that gaps between the second extension portion and the second clamping portions are filled, whereby the resin is prevented from leaking from between the second extension portion and the second clamping portions. joining one metal plate having a plurality of terminals, a first connection portion that connects the plurality of terminals to each other, a first extension portion disposed on one end of the first connection portion to extend from the first connection portion in a first direction beyond the plurality of terminals, and a second extension portion disposed on the other end of the first connection portion 11 to extend from the first connection portion in a second direction opposite to the first direction and beyond the plurality of terminals, and another metal plate having an electronic component mounted thereon and having a first fitting portion comprising a pair of first clamping portions configured to clamp the first extension portion, and a second fitting portion comprising a pair of second clamping portions configured to clamp the second extension portion thereby joining the first and second metal plates (10, 50) together; and sealing the mounted component with a resin by using a mold, the mold comprising; a pair of first protrusion portions to press each portion of the pair of first clamping portions, respectively; and a pair of second protrusion portions to press each portion of the pair of second clamping portions respectively, wherein: in the step of sealing the mounted component with the resin, each portion of the pair of first clamping portions is pressed to be extended by the respective one of the pair of first protrusion portions, so that gaps between the first extension portion and the first clamping portions are filled, whereby the resin is prevented from leaking from between the first extension portion and the first clamping portions, and each portion of the pair of second clamping portions is pressed to be extended by the respective one of the pair of second protrusion portions, so that gaps between the second extension portion and the second clamping portions are filled, whereby the resin is prevented from leaking from between the second extension portion and the second clamping portions. in the step of sealing the mounted component with the resin, each portion of the pair of first clamping portions is pressed to be extended by the respective one of the pair of first protrusion portions, so that gaps between the first extension portion and the first clamping portions are filled, whereby the resin is prevented from leaking from between the first extension portion and the first clamping portions, and each portion of the pair of second clamping portions is pressed to be extended by the respective one of the pair of second protrusion portions, so that gaps between the second extension portion and the second clamping portions are filled, whereby the resin is prevented from leaking from between the second extension portion and the second clamping portions.