A fuel supply device comprising: a fuel pump unit having a fuel pump which is disposed in a fuel tank and pumps up fuel in the fuel tank, thereby pumping the fuel to an internal-combustion engine, and a support section which fixes the fuel pump to an inner wall surface of the fuel tank; and a suction filter which is mounted on a fuel suction section provided at the fuel pump unit and filters the fuel that is suctioned into the fuel pump, wherein the suction filter has a connecting pipe (38, 138) which protrudes toward the fuel pump unit, a filtering medium of the suction filter is disposed so as to face the bottom surface of the support section, at both the fuel pump unit and the connecting pipe (38, 138), fixing mechanisms (42, 51, 142, 151) are provided which maintain a connection state of the connecting pipe (38, 138) in cooperation with each other in a case where the connecting pipe (38, 138) has been rotated around an axis thereof in a state where the connecting pipe (38, 138) has been connected to the fuel suction section, each of the fuel suction section and the connecting pipe (38, 138) has a tubular shape and also the connecting pipe (38, 138) is connected to the fuel suction section, the fixing mechanisms (42, 51, 142, 151) include a first engagement section (42, 142) provided on the suction filter side, and a second engagement section (51, 151) which is formed at the fuel pump unit characterized in that: the connecting pipe (38, 138) is coaxially connected to the fuel suction section in a state of being able to come into contact with the bottom surface of the support section, the second engagement section (51, 151) is configured to accept the first engagement section (42, 142) from a circumferential direction, thereby being engaged with the first engagement section, (42, 142) the first engagement section (42, 142) extends in a circumferential direction of the connecting pipe (38, 138), is elastically deformable, and is provided with a projection which restricts falling-out from the second engagement section (51, 151), and the second engagement section (51, 151) has a falling-out prevention portion which prevents dropping-out of the suction filter in an axial direction. a fuel pump unit having a fuel pump which is disposed in a fuel tank and pumps up fuel in the fuel tank, thereby pumping the fuel to an internal-combustion engine, and a support section which fixes the fuel pump to an inner wall surface of the fuel tank; and a suction filter which is mounted on a fuel suction section provided at the fuel pump unit and filters the fuel that is suctioned into the fuel pump, wherein the suction filter has a connecting pipe (38, 138) which protrudes toward the fuel pump unit, a filtering medium of the suction filter is disposed so as to face the bottom surface of the support section, at both the fuel pump unit and the connecting pipe (38, 138), fixing mechanisms (42, 51, 142, 151) are provided which maintain a connection state of the connecting pipe (38, 138) in cooperation with each other in a case where the connecting pipe (38, 138) has been rotated around an axis thereof in a state where the connecting pipe (38, 138) has been connected to the fuel suction section, each of the fuel suction section and the connecting pipe (38, 138) has a tubular shape and also the connecting pipe (38, 138) is connected to the fuel suction section, the fixing mechanisms (42, 51, 142, 151) include a first engagement section (42, 142) provided on the suction filter side, and a second engagement section (51, 151) which is formed at the fuel pump unit the connecting pipe (38, 138) is coaxially connected to the fuel suction section in a state of being able to come into contact with the bottom surface of the support section, the second engagement section (51, 151) is configured to accept the first engagement section (42, 142) from a circumferential direction, thereby being engaged with the first engagement section, (42, 142) the first engagement section (42, 142) extends in a circumferential direction of the connecting pipe (38, 138), is elastically deformable, and is provided with a projection which restricts falling-out from the second engagement section (51, 151), and the second engagement section (51, 151) has a falling-out prevention portion which prevents dropping-out of the suction filter in an axial direction.