PURPOSE: To prevent a patient's body from being dislocated toward legs by repeating operation for raising his/her back.

CONSTITUTION: A back bottom is divided into the first back bottom 4a corresponding to a patient's back, and the second back bottom 4b positioned near his/her waist. The second back bottom 4b is mounted on the support frame 8 of the first back bottom 4a in such a way as capable of displacement, and one end of the support frame of the second bottom 4b is flexibly jointed to a waist bottom 5. The waist bottom 5 is fixed to and supported on a frame. The end of the support frame 8 of the first back bottom 4a is movingly coupled to a slit 12 formed on a back bottom rest 11 so as to be directed obliquely upward and toward a head board 13. According to this construction, the patient' s body can be prevented from being dislocated toward legs and a comfortable lying posture on a bed can be ensured.