There is no standard for the awareness of standing posture in stabilometry, yet little research addressing the matter has been carried out. In the present study, we evaluated the influence of different instructional sets during a test on stabilometry. Stabilometry was performed on 349 male subjects. Two different instructions were prepared for the subjects regarding the awareness of their standing posture. These instructions were a) "Please relax when you stand" (R-standing), and b) "Please make an effort to minimize your body sway" (E-standing). Subjects were classified into four groups according to the combination of these instructions they received. For the five body sway parameters, a comparison between R-standing and E-standing was performed, controlling for possible confounders such as age, height, body weight, educational history, alcohol consumption, and smoking status. The sway length in E-standing was larger than that in R-standing, even after the adjustment for possible confounders. Our results indicate that the difference in the instructional set caused a significant measurement bias. Thorough-going unification of instructions for the stabilometry should be recommended when stabilometry is performed in an epidemiological investigation.