A subject information acquiring apparatus includes a subject-holding member which holds a subject and a probe unit having a transducer which receives acoustic waves from the subject through the subject-holding member, a housing which accommodates the transducer, and a matching liquid-holding member configured to hold a matching liquid between the transducer and the subject-holding member, the probe unit being allowed to move relative to the subject-holding member. The probe unit has a guide which introduces the matching liquid to the subject-holding member, the matching liquid having been spilled from a space defined by the matching liquid-holding member, the transducer, and the subject-holding member onto the upper surface of the hosing and then flowed from the upper surface of the housing.