A tensile testing device includes a supporting unit, a cantilever unit and a connecting unit. The supporting unit defines a plurality of mating elements secured thereon for mating with a detected element. The cantilever unit is connected with the detected element by a lead for reading the tension. The connecting unit includes a penal attached on a lateral surface of the supporting unit, a turning plate pivotally installed on a front surface of the panel and rotated around a first axis which is perpendicular to the lateral surface, a first connecting block fastened to a front surface of the turning plate, and a second connecting block of which rear end pivotally connects the first connecting block and turns around a second axis perpendicular to the first axis.