To reduce cost by reducing the number of part items, by easily replacing a drain pipe, by coping even with a variation in a tank diameter.

This tank with a drain discharge device discharges a drain (d) gathered in the tank via the drain pipe 5 by a pressurizing atmosphere in the tank 1, by arranging the drain pipe 5 in the tank 1, and has the drain discharge device formed by arranging an opening-closing mechanism 11 in an end part of a drain discharge part 5a of a flexible pipe, by fastening and fixing the flexible pipe to an opening 4a by a fastening device 9, by inserting the flexible pipe into the opening 4a bored on a tank wall surface, by integrally constituting a drain sucking-up part 5b arranged in the tank 1 and the drain discharge part 5a arranged outside the tank 1, out of the one flexible pipe.