An apparatus is provided for washing and disinfecting a medical instrument with a duct. The apparatus comprises an accommodating member on which the medical instrument is accommodated and a bath member providing a washing bath in which the accommodating member is placed. The apparatus further comprises a washing unit washing at least the duct of the medical instrument accommodated on the accommodating member and placed in the washing bath and a brushing unit detachably mounted on the bath member and formed to have a brush brushing an inside of the duct when the endoscope is washed and disinfected by the washing unit.