For further improvement of indoor environments concerning air and noise pollutions, ventilation is one of the key factors. In this study, we develop the measuring technique of unsteady pressure on a rotating blade surface, to reveal the basic features of a cross-flow impeller. Specifically speaking, we consider the simplest model as the fundamental study, namely, the flow around the cross-flow impeller rotating with flat-plate blades in open space without any casings. On this impeller's blade, we measure the fluctuating pressures, which are discussed in comparison with flow visualizations with the particle-image velocimeter (PIV), velocity measurements by a hot-wire velocimeter (HW) and numerical simulations. As a result, by the compensation of the centrifugal-force effect, we get accurate pressures on the rotating blade, which are conditionally-averaged over a number of periods. The obtained experimental results can be also dedicated to CFD as standard benchmarks.