Legume-derived, and particularly soybean-derived, water-soluble polysaccharides are added to thickener-containing powder supplied with an instant food to prevent clumping of powder masses during reconstitution and for a more homogeneous reconstitution. Thus, the problem is solved which is encountered with soup powders such as a thickened soup powder and a curry-seasoned soup powder, which are supplied with instant foods such as instant noodles, containing thickeners such as starch or gum substances to impart thickness, whereby reconstitution in a stationary state produces swelling of the thickener and prevents adequate dispersion, resulting in scattering of powder masses in the soup and clumping at the bottom of the container and, thereby, impairing the taste.