A regenerative braking device (16, 20, 53a, 53b, 53c) of a dump truck comprising: an engine, a first generator and a second generator driven by the engine, at least one travel motor (10L, 10R) driven by generated electric power of the first generator, and at least one fan motor to which generated electric power of the second generator is inputted via a first rectifier circuit, the regenerative braking device (16, 20, 53a, 53b, 53c) comprising: at least one resistive element (53a, 53b, 53c) to which regenerating electric power from the at least one travel motor (10L, 10R) in regenerative braking is supplied and which is cooled by at least one fan driven by the at least one fan motor and converts electric energy into heat energy and dissipates heat; characterised in that it comprises a DC/DC converter that in puts a part of the regenerating electric power which is supplied to the at least one resistive element (53a, 53b, 53c) to an output line of the first rectifier circuit via a second rectifier circuit; a voltage line (61a, 61b) that extracts a voltage, which is lower than a voltage applied to the at least one resistive element (53a, 53b, 53c), from the at least one resistive element (53a, 53b, 53c) to apply the extracted voltage to a primary side of the DC/DC converter, wherein the voltage line (61a, 61b) is provided on a position such that a secondary side open-circuit voltage (V20 open) of the DC/DC converter exceeds an output side open-circuit voltage (V17 open) of the first rectifier circuit. an engine, a first generator and a second generator driven by the engine, at least one travel motor (10L, 10R) driven by generated electric power of the first generator, and at least one fan motor to which generated electric power of the second generator is inputted via a first rectifier circuit, the regenerative braking device (16, 20, 53a, 53b, 53c) comprising: at least one resistive element (53a, 53b, 53c) to which regenerating electric power from the at least one travel motor (10L, 10R) in regenerative braking is supplied and which is cooled by at least one fan driven by the at least one fan motor and converts electric energy into heat energy and dissipates heat; at least one resistive element (53a, 53b, 53c) to which regenerating electric power from the at least one travel motor (10L, 10R) in regenerative braking is supplied and which is cooled by at least one fan driven by the at least one fan motor and converts electric energy into heat energy and dissipates heat; a DC/DC converter that in puts a part of the regenerating electric power which is supplied to the at least one resistive element (53a, 53b, 53c) to an output line of the first rectifier circuit via a second rectifier circuit; a voltage line (61a, 61b) that extracts a voltage, which is lower than a voltage applied to the at least one resistive element (53a, 53b, 53c), from the at least one resistive element (53a, 53b, 53c) to apply the extracted voltage to a primary side of the DC/DC converter, wherein the voltage line (61a, 61b) is provided on a position such that a secondary side open-circuit voltage (V20 open) of the DC/DC converter exceeds an output side open-circuit voltage (V17 open) of the first rectifier circuit.