Flow field around the perforated cube placed on the flat plate has been investigated using a water tunnel experimentally. Observation around a cube of various open area ratios has been made by the dye method and the hydrogen bubble method. The pattern are photographed from upper side, in order to make clear the mechanism of the change of patterns with varying the open area ratio. With increasing the open area ratio, the hydraulic shadow is narrow and an adverse pressure gradient upstream the model is weak. Futhermore the frequency of the vortex shedding from side wall of the cube are large with increasing the open area ratio.