An oil and sludge collecting tank is disclosed, which can be placed on-site at a food factory or the like, that discharges oil-containing wastewater, and which can collect oil and sludge more efficiently from an upper layer of an oil/water separation tank that pools the oil-containing wastewater. The oil and sludge collecting tank temporarily stores an upper layer of an oil/water separation tank, and collects oil and sludge. The oil and sludge collecting tank comprises: an upper tank TA into which the upper layer of the oil/water separation tank flows through an inflow pipe; at least one or more lower tank TB that has a smaller volume than the upper tank TA, and that is continuously provided from the bottom surface of the upper tank TA; and a lower tank heating section H2 that heats the lower tank TB.