A body lifting device for a bed is provided with a support unit, having a predetermined height, connected to a fixing part of a bed. A movable bed part adjusts an angle between the fixing and movable parts. A driving force transfer member of the device is connected to the movable part at one end, the other end extending toward the fixing part, and has a support point therebetween supported by the support unit. A length between the support point and the other end varies depending on an angle adjustment of the movable part. A lifting unit of the device supports a portion of a user's body, and is connected to the other end of the driving force transfer member. The lifting unit selectively lifts up the user's body depending on movement of the driving force transfer member, which is caused by adjusting an angle of the movable part.