To provide a waste gasoline treatment device safely burning gasoline.

The waste gasoline treatment device S includes a mixing tank 1 mixing water, a surfactant, and waste gasoline, and reserving the mixed liquid, a burner 5, a first passage 6 connecting the mixing tank 1 and a fuel supply passage 51 of the burner 5, a first pump arranged in the middle of the first passage 6 and guiding the mixed liquid in the first passage 6 to the fuel supply passage 51 of the burner 5, a second passage 8 connecting the middle of the first passage 6 and the mixing tank 1, a second pump 9 arranged in the middle of the second passage 8 and guiding the mixed liquid in the second passage 8 to the mixing tank 1, and a switch 10 for guiding the mixed liquid in the first passage 6 by selectively switching over to the fuel supply passage 51 of the burner 5 or to the second passage 8.