A filter device for transmission oil has a filter element (24) insertable into a transmission oil pan (70) with a filter medium (32) separating an unfiltered side from a filtrate chamber connected to an outlet (38, 50, 72), to which a suction oil pump can be connected. The filter medium (32) has a first structural layer (46) having a predetermined surface area and predeterminable filter properties and has a second structural layer (44, 60) having predeterminable filter properties. The surface area of the second structural layer (44; 60) is different from the surface area of the first structural layer (46). The structural layers (44, 46, 60) encompass an inner filter cavity (30) and are pleated having the same type of pleats. The pleated structural layers (44, 46, 60) extend in axial alignment between two end caps (22, 34) of the filter element (24). Viewed in the flow direction of the fluid flow to be cleaned, the structural layers (44, 60) having the higher filtration grade are downstream of an upstream structural layer (46) having a lower filtration grade.