An ultrasound diagnostic adapter used when diagnosing a subject using an ultrasound probe that transmits and receives ultrasound waves, the ultrasound diagnostic adapter includes: a pad which has (i) a main surface that is a surface on a side where the ultrasound probe is disposed, and (ii) a back surface that is a surface which is opposite to the main surface and is on a side where the subject is disposed and a first reflective member which is disposed inside the pad and made from a material having a different acoustic impedance than a material included in the pad, wherein the first reflective member is disposed such that at least one of (i) a distance between the first reflective member and the main surface and (ii) a width of the first reflective member viewed from the side of the main surface varies depending on a position in the main surface.
