What’s the difference between the Metropolitan Police Department and the National Police Agency?
Unlike the 警視庁, who look at things, this is just the police officer (警察) agency. Just the general police agency of the whole country, making them part of the National Police Agency.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.