A heat-exchanging ventilation device to perform ventilation while exchanging heat between a supply airflow and a discharge airflow, the heat-exchanging ventilation device comprising: a casing; a heat exchanger including a heat exchange element having a prism shape and accommodated in the casing to be insertable into and removable from the casing; a plurality of support members to support the heat exchanger in the casing; and a rotational force applying unit to apply a rotational force to the heat exchanger and rotate the heat exchanger, wherein when a rotational force is applied to the heat exchanger in one direction by the rotational force applying unit, the heat exchanger is pressed against the support members, and when application of a rotational force in the one direction by the rotational force applying unit is stopped, the heat exchanger becomes rotatable in another direction, wherein the heat exchanger includes a frame member attached to a side extending in an axial direction of the heat exchange element, and the support members are located surrounding the heat exchanger and support the frame member, wherein the support members include a plurality of fixed rails (31, 32) fixed to the casing, wherein the fixed rails (31, 32) include a first contact portion (31a, 32a) that extends in the axial direction of the heat exchange element, is formed in front of the frame member in the one direction, and is capable of coming into contact with the frame member, characterized in that the support members include a plurality of movable rails (33, 34) supported by the casing or a member fixed to the casing such that the movable rails (33, 34) are movable in a direction perpendicular to the axial direction of the heat exchange element, the movable rails (33, 34) include a second contact portion (33a, 34a) that extends in the axial direction of the heat exchange element, is formed in front of the frame member in the another direction, and is capable of coming into contact with the frame member, and the rotational force applying unit is the movable rails (33, 34) that are configured to move in the direction perpendicular to the axial direction of the heat exchange element such that the rotational force presses the second contact portion (33a, 34a) against the frame member to support the heat exchanger by the support members in the casing. a casing; a heat exchanger including a heat exchange element having a prism shape and accommodated in the casing to be insertable into and removable from the casing; a plurality of support members to support the heat exchanger in the casing; and a rotational force applying unit to apply a rotational force to the heat exchanger and rotate the heat exchanger, wherein when a rotational force is applied to the heat exchanger in one direction by the rotational force applying unit, the heat exchanger is pressed against the support members, and when application of a rotational force in the one direction by the rotational force applying unit is stopped, the heat exchanger becomes rotatable in another direction, wherein the heat exchanger includes a frame member attached to a side extending in an axial direction of the heat exchange element, and the support members are located surrounding the heat exchanger and support the frame member, wherein the support members include a plurality of fixed rails (31, 32) fixed to the casing, wherein the fixed rails (31, 32) include a first contact portion (31a, 32a) that extends in the axial direction of the heat exchange element, is formed in front of the frame member in the one direction, and is capable of coming into contact with the frame member, characterized in that the support members include a plurality of movable rails (33, 34) supported by the casing or a member fixed to the casing such that the movable rails (33, 34) are movable in a direction perpendicular to the axial direction of the heat exchange element, the movable rails (33, 34) include a second contact portion (33a, 34a) that extends in the axial direction of the heat exchange element, is formed in front of the frame member in the another direction, and is capable of coming into contact with the frame member, and the rotational force applying unit is the movable rails (33, 34) that are configured to move in the direction perpendicular to the axial direction of the heat exchange element such that the rotational force presses the second contact portion (33a, 34a) against the frame member to support the heat exchanger by the support members in the casing.