A toilet cleaning system, comprising: a water supply channel (19, 8) configured to supply cleaning water to a plurality of toilets; a bypass water supply channel which is branched from the water supply channel (19,8) 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 (19, 8) configured to supply cleaning water to a plurality of toilets; a bypass water supply channel which is branched from the water supply channel (19,8) 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.