A murder inquiry has been launched after the bodies of five people were found in a flat north-east of Paris.
The victims are a woman and her four children aged between nine months and 10 years old, prosecutors say.
Their bodies were found late on Monday evening in the town of Meaux, 40km (25 miles) from the French capital.
Police were looking for the 33-year-old father and on Tuesday arrested a man, French media report.
Relatives raised the alarm after they failed to receive any response from the family.
Prosecutor Jean-Baptiste Bladier confirmed to French media that the Versailles judicial police service was investigating.
The flat showed no sign of break-in and the children's father was not present, he said.
The Paris region has recently seen a series of infanticides:
In late November, a 41-year-old man confessed to killing his three daughters, aged four, 10 and 11, and turned himself in. Police found them dead in his home in the town of Alfortville, in the south-eastern suburbs of the capital
In October, a policeman killed his three daughters before killing himself at his home in Vemars in Val-d'Oise.
