PURPOSE: To substantially maintain storage of a powder chamber, transportation, and distribution of a drop unit, by improving stability of the drop unit, particularly of a mine without sharply altering an outer configuration of the same.

CONSTITUTION: Each righting element 7 includes a final end link 8 and at least one intermediate link 9, and the final end link 8 and the intermediate link 9 are pivoted and coupled with each other at a common turning support point A, and further there is provided at least one guide link 11 for causing the final end link 8 to perform a predetermined motion upon straddling and the straddling motion of the final end link 8 is restricted at a final end position.