To accurately assemble a prescribed window frame even if there is some error on the opening section of a sandwich panel forming a window.

This window frame device for a fixed sash window is provided with four bead fixing frame members 3 fitted at the peripheral edge of the square opening section of a panel 1, the first rectangular connecting metals rectangularly connecting the adjacent bead fixing frame members 3 together, and two pairs of four beads 5 coupled with the corresponding bead fixing frame members 3 and butted with adjacent end sections inclined by 45° against the longitudinal direction and the second rectangular connecting metals 6 rectangularly connecting the adjacent beads 5 together.