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Effects of the cylinder wake in a freestream on joint velocity statistics of a turbulent boundary layer over a flat plate are investigated by means of wind tunnel experiments. The cylinder is set horizontally over the flat plate and the interactions between its wake and the zero-pressure-gradient turbulent boundary layer are investigated. The locations of the cylinder are varied in total 9 cases. The unit Reynolds number is Re = U0 / v = 7.38 × 105m-1 and the Reynolds number based on the momentum thickness at the measuring location is Reθ = 3,140, where U0 is the uniform inlet velocity and v is the kinematic viscosity. Instantaneous two component velocities are measured using hot-wire anemometry with an X-probe. The results show that the streamwise and vertical rms velocities and the Reynolds streeses are suppressed by the cylinder wake for all the cases. The decrease in vertical rms velocity is less significant in comparison with that in streamwise rms velocity. The four-quadrant analysis of the Reynolds shows that the Reynolds stresses in the 2nd and 4th quadrants are decreases by the cylinder wake, whereas changes in the 1st and 3rd quadrants are very small. The cospectra of fluctuating velocity components, u and v, are suppressed in the entire frequency region by the cylinder wake.