To provide a filter membrane which makes openings less likely to be closed, can obtain data having good reproducibility, and achieves excellent mechanical characteristics.SOLUTION: A filter membrane comprises: a first layer 11 having a first surface to which a treatment medium is supplied； a third layer 13 having a second surface opposite to the first surface； and a second layer 12 located between the first layer and the third layer. The first layer 11 comprises: first protruding parts 11a in which a cross sectional area gradually reduces from the second layer 12 side to the first surface 11 and first recessed parts 11b. The third layer 13 comprises: second protruding parts 13a in which a cross sectional area gradually reduces from the second layer 12 side to the second surface and second recessed parts 13b. The second protruding parts 13a respectively formed around the second recessed parts 13b scattered in an island-like form are connected to each other. Through holes 12b, each of which leads to the first recessed part 11b and the second recessed part 13b, are formed in areas of the second layer 12 where the second recessed parts 13b are formed. The first recessed parts 11b formed in at least areas facing the second protruding parts 13a are connected to each other. A cavity 13c is formed at an interior of each second protruding part 13a.SELECTED DRAWING: Figure 1【課題】開口が塞がりにくく、再現性のよいデータを得ることができる機械的特性に優れるフィルタ膜の提供。【解決手段】処理媒体が供給される第１表面を有する第１層１１と第１表面と反対側の第２表面を有する第３層１３と第１層と第３層との間の第２層１２とから構成され、第１層１１には第２層１２側から第１表面に向かって、第３層１３には第２層１２側から第２表面に向かって断面積が次第に小さくなる第１凸部１１ａ及び第２凸部１３ａと、第１凹部１１ｂ、第２凹部１３ｂとから構成され、島状に散在する第２凹部１３ｂの周囲に形成された第２凸部１３ａは互いに繋がっており、第２層１２の第２凹部１３ｂが形成された領域には第１凹部１１ｂと第２凹部１３ｂとの貫通孔１２ｂが形成され、少なくとも第２凸部１３ａに対向する領域に形成された第１凹部１１ｂは互いに繋がり合っており、第２凸部１３ａの内部には空洞１３ｃが形成されているフィルタ膜。【選択図】図１
