Abstract: A packing device made of thermo-formed plastic sheet includes a bottom plate having adjacent first recesses and each first recess has first flaps which are higher than a receiving plane of the first recess, and each first recess has a positioning portion in an inside thereof. A side plate being foldable along a folding line relative to the bottom plate has engaging portions which are engaged with the positioning portions. The side plate includes adjacent second recesses and each second recess has a plurality of second flaps which are higher than a receiving plane of the second recess. The side plate has receiving portions located opposite to the engaging portions. A top plate being foldable along a folding line relative to the side plate has protrusions which are engaged with the receiving portions when the top plate is folded the folding line toward the side plate. The top plate has third recesses and each of which has third flaps which are higher than a receiving plane of the third recess.