The present invention relates to a waste water recycling system using a constant-temperature heat source tank, the system in which wastewater is converted into a heat source by separating various kinds of sewage and wastewater in site into sludge and wastewater, so that homeothermal property of wastewater is maintained by allowing a heat exchange between underground water and the wastewater; sludge is converted into solid fuel by drying the sludge using heat energy obtained from the wastewater; heat is supplied to a purifying plant greenhouse and a workplace, etc.; the wastewater used for heat source may be recycled into a purified water after used for growing purifying plants. The present invention provides the above-mentioned apparatus including: a dewatering unit (10) receiving sewage waste, separating into wastewater and sludge, and discharging the separated wastewater and sludge; one or more constant-temperature heat souce tank (20) including a wastewater storage tank (21) storing the wastewater discharg
