This paper presents a single-degree-of-freedom (single-DoF) gravity balancer that can deal with variable payload without requesting manual or other auxiliary adjustment. The proposed design is an integration of two mechanism modules, i.e., a standard spring-based statically balanced mechanism and a spring adjusting mechanism. A tensile spring is attached to the statically balanced mechanism for balancing the payload, and its installation points are controlled by two cables, which are driven by the spring adjusting mechanism. When different payloads are applied, the spring adjusting mechanism will act to regulate the spring installation points to suitable places such that the overall potential energy of the mechanism and the (variable) payload remains constant within the workspace of the balancer. This therefore suggests the main novelty of the proposed design where the balancer mechanism can automatically sense and respond the change of the payload without manual adjustment to the balancing mechanism. A prototype is built up and successfully tested for the proposed concept.