A fluid filter comprising a housing, a releasable cover and a replaceable filter having a filter body and two end plates. The filter is placed on a housing standpipe which has on its free side, facing the cover, an axially displaceable endpiece. The endpiece is preloaded in the expulsion direction and in that position is blocked by a locking system against insertion which prevents the cover from connecting with the housing. An unlocking device guided by the filter unlocks the locking system and allows insertion of the endpiece. The locking system is formed by locking tabs which are radially movable, and each have a locking face facing in the axial direction. The tabs are preloaded in the locking direction and each lock the endpiece in its expelled position against axial insertion relative to the standpipe. The tabs can be radially moved into their unlocking position by the unlocking device.