To obtain the subject contrast medium for ultrasonic waves that is used for increasing the contrast of the diagnostic images in the ultrasonic water image diagnosis and can be targeted to specific sites in the body by allowing a biotin derivative to statically link to on the surface of specific fine foams.

(B) A biotin derivative is allowed to statically bond to the surfaces of dine foams that are coated with (A) a carboxylate salt. As a carboxylate salt (A), are used sodium laurate, sodium myristate, sodium palmitate, sodium stearate or sodium oleate, singly or in the form of a mixture. In a preferred embodiment, the component (B) is N-(2-aminoethyl)biotin amide hydrochloride represented by the formula.