A three-dimensional knit fabric comprising front and back knit layers and a connecting yarn consisting of monofilament for connecting the knit layers to each other, characterized in that the curvature of the monofilament in the three-dimensional knit fabric is in a range from 0.01 to 1.6, and the bending elongation of the monofilament is 20% or less when the three-dimensional knit fabric is compressed to 50%. The three-dimensional knit fabric has a cushioning property in springiness which does not deterilate even if the fabric is repeatedly used many times or for a long time, and thus this fabric is excellent in terms of durability of the cushioning property. In particular, the fabric is suitable for use as a hammock type seat and exhibits a cushioning property having a favorable springy feeling as well as a good fit feel. Thus, the fabric provides a cushion material having an excellent shape-retaining property. The cushioning material fit the sitting human body well, and exhibits minimized occurrence of deformation (depression) due to compressive force worked thereon by the user to sit thereon.