There is provided a radioactive sludge transfer apparatus for transferring sludge stored in a sludge storage tank with supernatant solution to a transfer tank including: a transfer apparatus body; a stifling apparatus for blasting the supernatant solution to the sludge to thereby produce sludge solution in the one tank; sludge solution transfer apparatus for transferring the sludge solution to the transfer tank; an attitude control float; a floating force control ballast tank; and control device for remotely controlling the stifling apparatus, the sludge solution transfer apparatus and the floating force control ballast tank.