The invention discloses a sewage collecting device of a lateral-loading type garbage compressing vehicle. The sewage collecting device comprises a box body, a rear door cover, a first sealing element and a sewage box. A garbage pouring opening is formed in the rear end of the box body, the rear door cover is arranged at the rear end of the box body, the first sealing element is arranged between the rear end of the box body and the front end of the rear door cover, the sewage box is arranged below the rear door cover, a sewage receiving opening is formed in the top of the sewage box, a plurality of sewage leaking holes corresponding to the sewage receiving opening are formed in a bottom plate of the rear door cover, the front end of the sewage receiving opening stretches forwards out of the front end of the bottom plate of the rear door cover, and when the rear door cover is closed, the front end of the sewage receiving opening is located below the first sealing element so that sewage leaked between the rear end of the box body and the first sealing element or between the front end of the rear door cover and the first sealing element can flow into the sewage box. By means of the sewage collecting device, sewage leaked in the collecting, transferring and parking process of the lateral-loading type garbage compressing vehicle can be avoided or reduced. The invention further discloses the lateral-loading type garbage compressing vehicle adopting the sewage collecting device.