To provide a locking device for an opening/closing member capable of easily correcting dispersion in dimensions and in installation of respective components such as a ventilation panel and of securely locking the opening/closing member.

The locking device includes a pair of upper and lower blocks 42, 40. The upper block 42 has a U-shaped opening 46, and the lower block 40 has a lower face 40a abutting on a mounting face 14c. The lower face of the upper block 42 and the upper face of the lower block 40 are inclined to a ventilation opening peripheral edge face 14b, and projecting/recessed parts 42c, 40c are provided on inclined faces 42b, 40b of the upper and lower blocks 42, 40. The upper and lower blocks 42, 40 are fixed to the mounting face 14c by engaging the projecting/recessed parts 42c, 40c with each other. By changing the engagement position of the upper and lower blocks 42, 40, a distance between the U-shaped opening 46 and the mounting face 14c is adjusted.