A suspension system for a traveling vehicle body is disclosed. The system includes a suspension reference position varying mechanism (18) for varying a reference position of a suspension stroke of the suspension mechanism (100), and a controller (35) configured to calculate an intermediate value from a maximal value corresponding to the maximal position of the suspension stroke and a minimal value corresponding to the minimal position of the suspension stroke, and to control the suspension reference position varying mechanism such that, when the calculated intermediate values deviates from a set target range, the intermediate value is displaced toward the target range. The controller (35) increases a control execution frequency for the suspension reference position varying mechanism (18) when the traveling speed of the vehicle body is low, and reduces the control execution frequency for the suspension reference position varying mechanism (18) when the traveling speed of the vehicle body is high.