An ultrasonic-transducer mounting structure comprising: a housing including: a body part which is formed into a hollow cylindrical shape and is provided at its front surface with a transmission surface allowing an ultrasonic wave to pass therethrough and is designed to accommodate an ultrasonic transducer therein; and plural connection pieces provided to a side surface of the body part; and a holder fixed to a rear surface of a bumper and designed to hold the housing such that the transmission surface of the housing is exposed via an opening of the bumper, wherein: the holder includes plural reception pieces to which the plural connection pieces are detachably coupled respectively; the plural reception pieces are fixed to the rear surface of the bumper to surround the opening; the holder includes plural fixed plates respectively corresponding to the plural reception pieces; each fixed plate has a first surface in a thickness direction and is fixed to the rear surface of the bumper at its first surface; each fixed plate has a second surface in the thickness direction to which the corresponding reception piece is provided; the reception piece protrudes from the second surface in the thickness direction of the fixed plate; the plural reception pieces each include a basement formed into a rectangular plate shape, a pedestal formed on a surface in a thickness direction of the basement, and a latching protrusion formed on a surface, in a thickness direction of the basement, of the pedestal, the plural connection pieces each include a first catching piece and a second catching piece which face each other and are spaced by an interval; the first catching pieces of the plural connection pieces each include a latching hole for receiving the corresponding latching protrusion; and the plural connection pieces are respectively detachably coupled to the plural reception pieces by inserting the plural reception pieces into the corresponding intervals between the first catching pieces and the second catching pieces of the plural connection pieces and by fitting the latching protrusions of the plural reception pieces into the corresponding latching holes. a housing including: a body part which is formed into a hollow cylindrical shape and is provided at its front surface with a transmission surface allowing an ultrasonic wave to pass therethrough and is designed to accommodate an ultrasonic transducer therein; and plural connection pieces provided to a side surface of the body part; and a holder fixed to a rear surface of a bumper and designed to hold the housing such that the transmission surface of the housing is exposed via an opening of the bumper, wherein: the holder includes plural reception pieces to which the plural connection pieces are detachably coupled respectively; the plural reception pieces are fixed to the rear surface of the bumper to surround the opening; the holder includes plural fixed plates respectively corresponding to the plural reception pieces; each fixed plate has a first surface in a thickness direction and is fixed to the rear surface of the bumper at its first surface; each fixed plate has a second surface in the thickness direction to which the corresponding reception piece is provided; the reception piece protrudes from the second surface in the thickness direction of the fixed plate; the plural reception pieces each include a basement formed into a rectangular plate shape, a pedestal formed on a surface in a thickness direction of the basement, and a latching protrusion formed on a surface, in a thickness direction of the basement, of the pedestal, the holder includes plural reception pieces to which the plural connection pieces are detachably coupled respectively; the plural reception pieces are fixed to the rear surface of the bumper to surround the opening; the holder includes plural fixed plates respectively corresponding to the plural reception pieces; each fixed plate has a first surface in a thickness direction and is fixed to the rear surface of the bumper at its first surface; each fixed plate has a second surface in the thickness direction to which the corresponding reception piece is provided; the reception piece protrudes from the second surface in the thickness direction of the fixed plate; the plural reception pieces each include a basement formed into a rectangular plate shape, a pedestal formed on a surface in a thickness direction of the basement, and a latching protrusion formed on a surface, in a thickness direction of the basement, of the pedestal, the plural connection pieces each include a first catching piece and a second catching piece which face each other and are spaced by an interval; the first catching pieces of the plural connection pieces each include a latching hole for receiving the corresponding latching protrusion; and the plural connection pieces are respectively detachably coupled to the plural reception pieces by inserting the plural reception pieces into the corresponding intervals between the first catching pieces and the second catching pieces of the plural connection pieces and by fitting the latching protrusions of the plural reception pieces into the corresponding latching holes.