A composition for an ultrasonic probe contains: a mixture including at least three different polyorganosiloxanes, in which the mixture includes (A) a polyorganosiloxane having a vinyl group, (B) a polyorganosiloxane having two or more Si—H groups in a molecular chain, and (C) a branched polyorganosiloxane represented by the following General Formula (C), and the content of the polyorganosiloxanes (A), (B), and (C) is respectively 10 to 99.4 parts by mass, 0.5 to 90 parts by mass, and 0.1 to 40 parts by mass, with respect to 100 parts by mass of the total mass of the polyorganosiloxanes mixture.
R1 to R4 each independently represent an alkyl group, a cycloalkyl group, an alkenyl group, or an aryl group. m represents an integer of 1 or more and n represents 0 or an integer of 1 to 5. At least two of a plurality of R4's are alkenyl groups.