The filter device (10) is provided with a drain device (50) provided with a main body (51) and a plug (60). The main body (51) has a first opening (51a) which communicates to the outer side of a housing (20), a second opening (51b) which communicates with an inner side (42a) of a filter element (40), and a third opening (56) which communicates with a first channel (51c) communicating to the first opening (51a) and the second opening (51b) and a space (B) between the filter element (40) and the housing (20). The plug (60) is held within the first channel (51c), and is movable between a first position (P1) at which fluid is not discharged from the housing (20), and a second position (P2) at which fluid is discharged from the housing (20). The plug (60) is provided with a second channel (65) that communicates with the first channel (51c) and communicates with the outer side of the housing (20) when in the second position (P2).