A cap unit attached to an opening of a bottle container containing puncture-sealing agent, and comprising a cap main body comprising an air flow passage to feed compressed air from a compressor into the bottle container through an air intake port,, and a sealing agent/compressed air extractive flow passage to extract the puncture-sealing agent and the compressed air from the bottle container in succession by the feed of the compressed air; wherein said cap main body is provided in an upper end part of the cap main body with an opening-attaching concave part for inserting and fixing of said opening of the bottle container, and with a boss part projecting from a basal plane of the openi ng-attachi ng concave part; an upper end face part of said boss part comprises an air flow passage upper opening forming an upper end of said air flow passage, and a sealing agent/compressed air extractive flow passage upper opening forming an upper openi ng of the seal i ng agent/compressed air extractive flow passage; said air flow passage is provided with a reversed flow preventing device to prevent from reversed flow of the puncture-sealing agent toward a compressor; said air flow passage comprises a vertical flow passage extending inferiorly from said air flow passage upper opening, a lateral flow passage extending laterally from said air intake port, and a connecting flow passage connecting them; and said cap main body comprises a vertical hole with steps, said reversed flow preventing device comprises a ball-shaped spherical valve inserted movably into the vertical hole and enabling to open and close the valve seat; characterized in that said steps of the vertical hole have internal diameters that increase downwardly in a stepwise manner, and the vertical hole including: a first vertical hole extending from said air flow passage upper opening, a second vertical hole leading toward the first vertical hole with a first step surface, a third vertical hole leading toward the second vertical hole with a second step surface, and a fourth vertical hole, leading toward the third vertical hole with a third step surface, having the lower end thereof opening in a basal plane of the cap main body, and being provided in a lower end pat with a securing groove extending in the circumferential direction; said vertical flow passage is formed of said first to third vertical holes, and a valve seat case comprising said connecting flow passage is inserted from the lower end of the fourth vertical hole and kept therein; said reversed flow preventing device comprises a ring-shaped valve seat disposed in an upper end of the valve seat case and connecting said vertical flow passage with said connecting flow passage, and a biasing spring disposed in said second vertical hole and biasing the spherical valve toward the valve seat; and said valve seat case is provided with a preventing dropping device to prevent dropping from the fourth vertical hole by an engagement with said securing groove. a first vertical hole extending from said air flow passage upper opening, a second vertical hole leading toward the first vertical hole with a first step surface, a third vertical hole leading toward the second vertical hole with a second step surface, and a fourth vertical hole, leading toward the third vertical hole with a third step surface, having the lower end thereof opening in a basal plane of the cap main body, and being provided in a lower end pat with a securing groove extending in the circumferential direction; said vertical flow passage is formed of said first to third vertical holes, and a valve seat case comprising said connecting flow passage is inserted from the lower end of the fourth vertical hole and kept therein; said reversed flow preventing device comprises a ring-shaped valve seat disposed in an upper end of the valve seat case and connecting said vertical flow passage with said connecting flow passage, and a biasing spring disposed in said second vertical hole and biasing the spherical valve toward the valve seat; and said valve seat case is provided with a preventing dropping device to prevent dropping from the fourth vertical hole by an engagement with said securing groove.