PROBLEM TO BE SOLVED: To provide a medical needle safety device capable of lifting (stretching) legs (31,32) in an upper direction by one action (step), thereby protecting (shielding) a sharp terminal of a needle member.SOLUTION: A first locking unit 40.1 forms a locking end 40.1T on a side engaging with a second locking unit 40.2, and the second locking unit (40.2) forms a plurality of projections (40T) and grooves (40M) between the projections on a side engaging with the locking end (40.1T). When legs (31, 32) are completely stretched in an almost vertical direction, the locking end 40.1T of the first locking unit 40.1 moves from a side of a first side part S1 to a side of a second side part S2 to lock at an end part on the side of the second side part S2.
