Roache faces an allegation of raping an underage girl in Lancashire between April and July in 1967, police said.
A Lancashire police spokesman said on Wednesday: "An 81-year-old man from Wilmslow in Cheshire has this morning, Wednesday May 1 2013, been arrested by Lancashire Constabulary on suspicion of rape.
"The man will be interviewed at a police station in Lancashire during the course of the day.
"We take all allegations of sexual abuse extremely seriously and would encourage people with any information about sexual abuse, or anyone who has been a victim of sexual abuse, to come forward and report their concerns confident in the knowledge they will be investigated appropriately and with sensitivity."
The 81-year-old is the longest serving cast member and only remaining member of the original show. He collected an award from Guinness World Records in 2010 for his achievement, having joined in 1960 for the series which was expected to last for just 13 episodes.
An ITV spokeswoman said the broadcaster was not in a position to comment, but it is understood Roache will not appear in the soap while investigations continue.
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