Over 150 police officers and 46 investigating magistrates took part in the operation carried out in 28 of Spain's 50 provinces.
Police said they searched 59 homes and seized over 170 computer hard drives, as well as 614 CDs and DVDs, which contained pornographic images.
The authorities are examining the material to see if any of the men who were detained sexually abused minors themselves.
Police said several of the suspects had been arrested in the past for exchanging pornographic images involving minors over the internet.
Macrooperación policial contra la pornografía infantil, hay 56 pedófilos detenidos por distribuir imágenes de abusos a niños de corta edad pic.twitter.com/iNTuzlkQJi— Policía Nacional (@policia) November 10, 2016
There were no further details and police did not identify any of the suspects. But police were to hold a press conference on the raids later on Thursday.
In August Spanish police arrested seven people, mainly French and Moroccan nationals, who were suspected of running a ring that produced pornography involving children.
The authorities suspect the ring exploited at least 80 minors during the past 15 years and distributed over a million pictures and videos of pornography and over a thousand DVDs.