Send help, a production crew member texted a friend after she revealed that she was "trapped" in actor Kang Ji-hwan's house.
She had gone there with another female crew member on Tuesday (July 9) night after the trio attended a company dinner, where they had many drinks.
When the police, who were alerted, arrived at the house, Korean media reported that they found the trio in the same room, and had to separate Kang, 42, from the women.
Questioned by the police, he said he had got drunk and had no recollection of what he had done.
Kang admitted that he drank with the women and woke up to discover that he was in the same room where the latter were sleeping.
But the women told a different story.
One of them said she woke up and saw Kang attempting to have sex with her colleague who was out cold.
She screamed in a bid to stop the assault.
She told police that she suspected she might have been a victim too, since her clothes were in a messy state.
Kang is now in detention, with the police set to interrogate him further.
The authorities are also seeking a pre-trial detention warrant.
His agency, meanwhile, said he will step away for now from show business activities.
The producers of TV drama Joseon Survival, which stars the actor, said the latest episode will not be broadcast, and that re-runs of previous episodes will not be aired.
It added that it is looking for another actor to take on Kang's role.
The two women are receiving help from Seoul Sunflower Centre, which offers support for victims of sexual violence.
The alleged assaults are the latest chapter in a scandal that has rocked the Korean entertainment industry from the start of the year.
Artists, from former BigBang singer Seungri to Jung Joon-young, have been hauled up for offences, from procuring prostitutes for would-be investors to tax evasion and sharing of sex videos in chatrooms.
In the incident involving Kang, netizens have also slammed those who wondered why the woman chose to call a friend, and not the police, for help.
They said victim-blaming is one reason many women shy away from taking sexual predators to task.