This paper presents a newly designed apparatus which can be used to measure the deformation of the cross-sectional area of circular tubes subjected to cyclic bending. The measurement apparatus is composed of eight LVDTs, which are symmetrically set on the circumference of the tube. Based on the detected signals from these eight LVDTs, the deformation of the tube cross section can be obtained. In addition, the eight LVDTs can be adjusted in the radial direction. Therefore, the section deformation of different sizes of circular tubes can be determined. In this paper, two different sizes of SUS 304 stainless steel tubes under curvature-controlled cyclic bending were used to test the newly designed apparatus. It has been shown that the deformation at eight different points of each tube cross-section was detected during the loading process. Thus, based on the detected data, the deformation of each tube's cross-section was properly described.