Abstract: To provide a simple-structured check valve unit that allows for retention of a seat relief in an attachment part of a plunger bore, facilitates production without increasing components, and prevents deformation of the plunger. The check valve unit includes the seat relief and a cap member. The plunger has an outlet relief hole in the attachment part for communication between the inside and outside of the plunger. The cap member includes a cap top, an oil flow portion, and a skirt wall. The skirt wall includes a plurality of outwardly raised contact surfaces and a plurality of inwardly raised contact surfaces. The circumscribed circle of the outwardly raised contact surfaces has a larger radius than the inside radius of the attachment part, and the inscribed circle of the inwardly raised contact surfaces has a smaller radius than the outside radius of an engaging part of the seat relief.