A toilet cleaning system , comprising: a water supply channel configured to supply cleaning water to a plurality of toilets ; a bypass water supply channel which is branched from the water supply channel and is to be connected to a drainage channel connectable to a drainage portion of each of the toilets ; and an air bubble mixing portion which bubbles air and mixes fine air bubbles of micrometer order into the cleaning water to be supplied to the bypass water supply channel , wherein an end portion on a downstream side of the bypass water supply channel is connected to an end portion on an upstream side of a region of the drainage channel , the region extending in an approximately horizontal direction, wherein the air bubble mixing portion comprises: a pump which sucks the cleaning water in a water storage portion provided on an upstream side of the bypass water supply channel and sucks air introduced from an air introduction pipe provided on an upstream side, a dissolution tank which is connected to a discharge side of the pump and dissolves air into the cleaning water by pressurization of the pump , and a pressure release portion to release pressure for depressurization, the pressure release portion being provided on a downstream side of the dissolution tank , and wherein cleaning water mixed with the fine air bubbles is generated by depressurizing cleaning water with air dissolved under pressure. a water supply channel configured to supply cleaning water to a plurality of toilets ; a bypass water supply channel which is branched from the water supply channel and is to be connected to a drainage channel connectable to a drainage portion of each of the toilets ; and an air bubble mixing portion which bubbles air and mixes fine air bubbles of micrometer order into the cleaning water to be supplied to the bypass water supply channel , wherein an end portion on a downstream side of the bypass water supply channel is connected to an end portion on an upstream side of a region of the drainage channel , the region extending in an approximately horizontal direction, wherein the air bubble mixing portion comprises: a pump which sucks the cleaning water in a water storage portion provided on an upstream side of the bypass water supply channel and sucks air introduced from an air introduction pipe provided on an upstream side, a dissolution tank which is connected to a discharge side of the pump and dissolves air into the cleaning water by pressurization of the pump , and a pressure release portion to release pressure for depressurization, the pressure release portion being provided on a downstream side of the dissolution tank , and wherein cleaning water mixed with the fine air bubbles is generated by depressurizing cleaning water with air dissolved under pressure. a pump which sucks the cleaning water in a water storage portion provided on an upstream side of the bypass water supply channel and sucks air introduced from an air introduction pipe provided on an upstream side, a dissolution tank which is connected to a discharge side of the pump and dissolves air into the cleaning water by pressurization of the pump , and a pressure release portion to release pressure for depressurization, the pressure release portion being provided on a downstream side of the dissolution tank , and wherein cleaning water mixed with the fine air bubbles is generated by depressurizing cleaning water with air dissolved under pressure. <EOS>