Dan Schneider is addressing the allegations in the new Nickelodeon doc that paints him as a monster and wildly inappropriate with some in the cast ... and he's taking accountability.

The one-time Nickelodeon honcho sat down with former "iCarly" actor BooG!e Tuesday to offer up his formal response to toxic workplace claims made against him and the shows he created ... which was just addressed in full on the new documentary that's going viral.

Check it out ... DS says it was very hard for him to watch the new docuseries ... acknowledging some of his past behavior as embarrassing and regretful.

He added ... "I definitely owe some people a pretty strong apology."

The former TV exec -- who was the showrunner on several Nick shows back in the day -- realized how his actions impacted those who worked for him. He says he'd never do some of the on-set shenanigans he pulled back then today -- explaining ... "I’m embarrassed that I did it then. I apologize to anybody that I ever put in that situation."

Dan even agrees some of the questionable jokes written for his shows should be cut right now ... insisting he wrote the quips with children in mind -- and that there was no ill intent.

Through his reps, Dan has denied claims that the shows he oversaw purposefully sexualized its child stars -- like Ariana Grande, Amanda Bynes and Jennette McCurdy, among others.

His spokesperson stated Monday ... "Everything that happened on the shows Dan ran was carefully scrutinized by dozens of involved adults, and approved by the network. Had there been any scenes or outfits that were inappropriate in any way, they would have been flagged and blocked by this multilayered scrutiny.”

Drake Bell -- who spoke out about being molested by Nickelodeon dialogue coach Brian Peck in 'Quiet on Set' -- credited Dan as an ally after he spoke out about the abuse.

In the new sit-down, Dan talks about Drake and Peck as well ... getting emotional doing so.

He says he was devastated when he learned of Brian's behavior ... explaining he did not hire the dialogue coach for the network, but has regrets nonetheless on having him around. He even revealed that he helped Drake's mother pen her statement for Brian's sentencing trial.