A fuel supply device connected to a plurality of first injectors (1a-1d) and a plurality of second injectors (1e-1h), wherein the fuel supply device supplies fuel from a fuel tank to each of the first injectors and each of the second injectors, the first injectors inject the fuel into a first combustion chamber of a first cylinder group of an engine, the second injectors inject the fuel into a second combustion chamber of a second cylinder group of the engine, and each of the first injectors and each of the second injectors are piezo-injectors, the fuel supply device comprising: a medium pressure pump capable of adjusting the fuel from the fuel tank to a medium pressure and delivering the medium-pressure fuel; a high pressure pump capable of adjusting the fuel to a high pressure, which is higher than the medium pressure, and delivering the high-pressure fuel; a high pressure passage that connects the high pressure pump to each of the first injectors and each of the second injectors; a first return passage connected to each of the first injectors, wherein the first return passage is capable of transporting surplus fuel from each of the first injectors; a second return passage connected to each of the second injectors, wherein the second return passage is capable of transporting surplus fuel from each of the second injectors; a recovery passage that joins the first return passage and the second return passage at a junction (d), wherein the recovery passage returns the surplus fuel to the fuel tank; a back pressure valve arranged in the recovery passage, wherein the back pressure valve is capable of applying a back pressure to each of the first injectors and each of the second injectors; a medium pressure passage connected to the medium pressure pump; a connection passage (31a,31b) that connects the medium pressure passage to one of the first return passage, the second return passage, and a portion of the recovery passage upstream from the back pressure valve; and a check valve having a lower opening valve pressure than the back pressure and arranged in the connection passage, wherein the check valve permits the supply of fuel from the medium pressure passage to the first return passage and the second return passage and impedes the opposite. a medium pressure pump capable of adjusting the fuel from the fuel tank to a medium pressure and delivering the medium-pressure fuel; a high pressure pump capable of adjusting the fuel to a high pressure, which is higher than the medium pressure, and delivering the high-pressure fuel; a high pressure passage that connects the high pressure pump to each of the first injectors and each of the second injectors; a first return passage connected to each of the first injectors, wherein the first return passage is capable of transporting surplus fuel from each of the first injectors; a second return passage connected to each of the second injectors, wherein the second return passage is capable of transporting surplus fuel from each of the second injectors; a recovery passage that joins the first return passage and the second return passage at a junction (d), wherein the recovery passage returns the surplus fuel to the fuel tank; a back pressure valve arranged in the recovery passage, wherein the back pressure valve is capable of applying a back pressure to each of the first injectors and each of the second injectors; a medium pressure passage connected to the medium pressure pump; a connection passage (31a,31b) that connects the medium pressure passage to one of the first return passage, the second return passage, and a portion of the recovery passage upstream from the back pressure valve; and a check valve having a lower opening valve pressure than the back pressure and arranged in the connection passage, wherein the check valve permits the supply of fuel from the medium pressure passage to the first return passage and the second return passage and impedes the opposite.