This paper reports on a micro force plate for a fruit fly, which is fabricated by a high-resolution 3D printer. The conventional force sensors for tiny insects were highly sensitive but fragile and took much time to be fabricated. The proposed force plate achieves both high sensitivity and toughness via completely 3D supporting micro-springs and an external laser displacement meter. The plate structure integrated with the micro-springs is easily and reproducibly printed in a single process. When a fruit fly lands on a plate surface, the ground reaction force (GRF) is measured with force resolution less than 1/50 of the body weight from the plate displacement via the laser displacement meter. Our proposed device is helpful to evaluate the biomechanics of tiny insects.