An apparatus for opening and closing a trunk for a vehicle, may include a motor unit equipped with a motor, an inner tube provided outside the motor unit to surround the motor unit, with a plurality of protrusions protruding from an outer circumference of the inner tube, an outer tube provided outside the inner tube to surround the inner tube and including a threaded groove being indented along an inner circumference of the outer tube, a bar-shaped spindle having a threaded portion on an outer circumference thereof, and coupled to the motor unit to cause the threaded portion of the spindle to engage with the threaded groove of the outer tube when the motor may be rotated, thus allowing the spindle to perform translation simultaneously with rotation, and an elastic member-wound on an outer circumference of the outer tube.