The man is suspected of raping the woman early Saturday in Nokia, police say.
According to police, the woman was walking on Pinsiöntie at four in the morning when she noticed the man following her.
The woman had continued walking along Rounionkatu, along which, according to police, the man had grabbed the woman and forced her further away, where the suspected rape took place.
In addition to the woman, the situation has an outside witness.
According to police, both the woman and the witness have said the suspect is about 30 years old, skinny and about 180 cents tall.
At the time of the incident, he was wearing field pants and a black hoodie with his hood pulled over his head.