To provide a fermentation treating apparatus which is of an externally mixing type and allows the preadjustment of waste without making the apparatus large-sized and a fermentation treating method.

This fermentation treating apparatus 10 is provided with a mixer 16 for performing the preadjustment of organic waste, a fermentation tank 18 for treating the preadjusted organic waste by fermentation, a condensation means 26 for obtaining the condensate by treating the gas which is generated accompanying the fermentation treatment by condensation, and first sending- back means 30, L7 for sending back the condensate obtained by the condensation treatment to the mixer 16.