A body trunk supporter provided with: a belt-like lower band section that is adapted to be wrapped around and positioned at the pelvis of a user; an X-shaped stretchable middle band section that has a pair of lower end parts joined to the lower band section and that presses areas of the lumbar region of the user; and a pair of upper band sections that are jointed to a pair of upper end parts of the middle band section and that are adapted to be wrapped around and positioned at the chest of the user, wherein the pair of lower end parts of the middle band section are configured to be joined to areas ranging from positions that are immediately lateral to the pelvis of the user to adjacent anterior positions thereof in the lower band section; and the pair of upper band sections are configured to be separated from each other and to extend in bilaterally opposite directions in an unfolded state, and are configured to be wrapped around and positioned near fifth to tenth ribs of the chest of the user.