A man in his 20s was found dead in a cell at Pasila police station in Helsinki on Wednesday evening.
In a press statement, the Helsinki Police Department said the man's body was discovered during a regular round of inspections, and attempts to resuscitate him were not successful.
Reports of deaths in police custody in Finland are relatively rare, but this is the second such incident in Helsinki this week.
A 35-year-old man died in the same facility at Pasila station on Monday.
In its statement, the department said it regretted the two deaths and underscored the importance of both incidents being carefully investigated.
The Western Uusimaa Police Department will carry out the investigations into the two deaths, as it is standard police practice that a separate department takes over the investigation when a person dies in custody.