A police officer — someone employed to maintain public safety and order, often in uniform performing patrols, investigations, traffic control, etc.
警察官が交差点で交通整理をしている。
A police officer is directing traffic at the intersection.
彼は警察官として十年間勤めている。
He has worked as a police officer for ten years.
事件の目撃者は警察官に事情を説明した。
The eyewitness explained the circumstances to the police officer.