A heat/acoustic wave conversion unit, comprising: a heat/acoustic wave conversion component having a first end face and a second end face,; a low-temperature side heat exchanger that is disposed adjacent to a first end part of the heat/acoustic wave conversion component on the first end face side, the low-temperature side heat exchanger exchanging heat with the first end part; and a high-temperature side heat exchanger that is disposed adjacent to a second end part of the heat/acoustic wave conversion component on the second end face side, the high-temperature side heat exchanger receiving inflow of heated fluid and absorbing heat from the heated fluid, and supplying the heat to the second end part so as to keep the second end part at a state of higher temperature than at the first end part, characterized in that the heat/acoustic wave conversion component includes a partition wall that defines a plurality of cells extending from the first end face to the second end face, inside of the cells being filled with working fluid that oscillates to transmit acoustic waves, the heat/acoustic wave conversion component mutually converting heat exchanged between the partition wall and the working fluid and energy of acoustic waves resulting from oscillations of the working fluid, the hydraulic diameter HD of the heat/acoustic wave conversion component is 0.4 mm or less, where the hydraulic diameter HD is defined as HD=4xS/C, where S denotes an area of a cross section of each cell perpendicular to the cell extending direction and C denotes a perimeter of the cross section, let that the heat/acoustic wave conversion component has a length L from the first end face to the second end face, the ratio HD/L of the hydraulic diameter HD to the length L of the heat/acoustic wave conversion component is 0.005 or more and less than 0.02, and the high-temperature side heat exchanger includes: a heat-exchanging honeycomb structure having a partition wall that defines two or more cells which extend in the extending direction between two end faces, an opposed end face facing to the second end face of the heat/acoustic wave conversion component and a non-opposed end face facing to an opposite side from the heat/acoustic wave conversion component when viewed from the opposed end face, and which are filled with the working fluid internally so as to be a propagation path of acoustic waves due to oscillations of the working fluid; and an annular tube that surrounds a circumferential face of the heat-exchanging honeycomb structure, which extends between the two end faces, and that defines a channel through which the heated fluid flows, the annular tube including a structure body that is disposed in the channel to increase a contact area with the heated fluid, an inflow port into which the heated fluid flows, and an outflow port through which the heated fluid flows out, wherein at least one of the heat-exchanging honeycomb structure and the structure body of the annular tube is made of a ceramic material that contains SiC as a main component. a heat/acoustic wave conversion component having a first end face and a second end face,; a low-temperature side heat exchanger that is disposed adjacent to a first end part of the heat/acoustic wave conversion component on the first end face side, the low-temperature side heat exchanger exchanging heat with the first end part; and a high-temperature side heat exchanger that is disposed adjacent to a second end part of the heat/acoustic wave conversion component on the second end face side, the high-temperature side heat exchanger receiving inflow of heated fluid and absorbing heat from the heated fluid, and supplying the heat to the second end part so as to keep the second end part at a state of higher temperature than at the first end part, characterized in that a heat-exchanging honeycomb structure having a partition wall that defines two or more cells which extend in the extending direction between two end faces, an opposed end face facing to the second end face of the heat/acoustic wave conversion component and a non-opposed end face facing to an opposite side from the heat/acoustic wave conversion component when viewed from the opposed end face, and which are filled with the working fluid internally so as to be a propagation path of acoustic waves due to oscillations of the working fluid; and an annular tube that surrounds a circumferential face of the heat-exchanging honeycomb structure, which extends between the two end faces, and that defines a channel through which the heated fluid flows, the annular tube including a structure body that is disposed in the channel to increase a contact area with the heated fluid, an inflow port into which the heated fluid flows, and an outflow port through which the heated fluid flows out,