The drag and lift coefficients of a flat-plate elastic wing subjected to a pitching motion were experimentally measured, and the effect of deformation due to fluid force on such an aerodynamic coefficients were investigated by comparing the results with those of a rigid wing. In the case without pitching motion, it was found that both the coefficients of an elastic wing considerably decrease as the Reynolds number increase, which is enhanced as flexibility increases, whereas those of a rigid wing is almost constant within the Reynolds-number range tested here. In the case with pitching motion, in addition to the similar reduction of the drag coefficient in the elastic wing, phase lag of the drag and lift coefficients was observed between the rigid and the elastic wing.