Fluctuating pressure fields on the surface and in the wake of a circular cylinder at a Reynolds number of 3.7×10⁴ are investigated using a computer aided flow visualization technique. The phase averaged pressure distribution on a cylinder is obtained and oscillating lift and drag forces are evaluated. Then instantaneous pressure fields in the wake region are determined, from which the coherent structure of the wake flow is discussed. On the basis of these results, the variation of fluctuating forces in time is quantitatively related to the details of the wake flow such as instantaneous static pressure fields and vorticity fields.