The present invention provides a rainwater catchment apparatus that is easily installed without renovating a building. The rainwater catchment apparatus comprises a rainwater inlet for introducing rainwater, a flange portion engaged with a peripheral portion of a rainwater outlet serving as a leading end of a drainage canal formed in a building framework for introducing rainwater in the rainwater inlet, a drain portion for discharging excessive water exceeding a predetermined level to the drainage canal, a reservoir freely fitted into the drainage canal through the rainwater outlet, and a pumping mechanism for pumping water stored in the reservoir to the outside.