To provide a fluid filter for an automatic transmission, for achieving a smaller size while reducing the amount of a resin to be used by increasing the filter area of a filter material relative to the appearance size of the filter.

The filter includes a resin upper-side case member 2, a resin lower-side case member 3 forming a filter chamber 4 between the upper-side case member and itself, and a filter element 5 having the filter material 9 arranged in the filter chamber and a resin side plate 10 for holding the edge of the filter material. Between the lower end of the peripheral side wall of the upper-side case member and the upper end of the side plate, an upper-side joint part 16 is formed to join the upper-side case member to the side plate. Between the upper end of the peripheral side wall of the lower-side case member and the lower end of the side plate, a lower-side joint part 17 is formed to join the lower-side case member to the side plate.

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