A needle device (1) includes a shell (2), a needle unit (3) and an actuator (5) . The needle unit (3) includes an outer needle guide (32) and a needle member (31). The outer needle guide (32) has a piercing end (321) for penetrating into a biological body part. The needle member (31) is disposed in the shell (2) and the outer needle guide (32), has a needle tip (312) protruding from a front end (21) of the shell (2) and is movable relative to the shell (2) and the outer needle guide (32). The actuator (5) is responsive to a control signal to drive the needle member (31) and move the needle tip (312) between a protruding position, where the needle tip (312) prctrudes out of the piercing end (321) of the outer needle guide (32), and a retracing position, where the needle tip (312) is retracted back into the outer needle guide (32).