In this article, the design and development of a biaxial tensile test device and its specimen are described. The device, which was designed for evaluating the mechanical characteristics of a thin film specimen under in-plane uniaxial and biaxial tensile stress states, consists of four sets of a piezoelectric actuator, a load cell, a linear variable differential transformer (LVDT), and an actuator case including lever structures with displacement amplification function. The structures fabricated by wire electrical discharge machining are able to amplify the actuator’s displacement by a factor of 3.8 along the tensile direction. The biaxial test specimen prepared using conventional micromachining processes is composed of a cross-shaped film section and chucking parts supported by silicon springs. After square holes in four chuck parts are respectively hooked with four loading poles, the film section is tensioned to the directions where the poles get away from the center of the specimen. Tensile strain rate can be individually controlled for each tensile direction. Raman spectroscopic stress analyses demonstrated that the developed biaxial tensile test device was able to accurately apply not only uniaxial but also biaxial tensile stress to a single-crystal silicon (SCS) film specimen.