A ureal water tank (28), a storage of an aqueous urea solution, is located within a utility room (6G) in a right front section of a revolving frame (6), which is readily accessible from outside. In this instance, among a plurality of operating oil conduits (18), a working mechanism operating conduit (21) which supplies operating oil to a boom cylinder (5D) of a working mechanism (5) is arranged to run along exterior surfaces of the ureal water tank (28). Therefore, even if the ureal water tank (28) is located in a place with no heat source, the aqueous urea solution in the ureal water tank (28) can be stably kept in a heated state by utilization of heat of operating oil in circulation through the working mechanism operating conduit (21).