The bombing outside Swiss Inn hotel in North Sinai's provincial capital Al-Arish killed two policemen, a judge and a civillian, officials said.
Fourteen people have been wounded and they suffer medium to severe injuries, Ministry of Health spokesperson said.
A main coastal highway in the city has been shut down following the bombing.
Soon after a suicide bomber triggered the car blast, a militant set off an explosive vest while a third attacker sneaked into the hotel and shot dead the judge, the army said.
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The blast happened a day after the second round of a parliamentary election closed in Egypt. The polls were the first legislative vote since the military overthrew former president Mohammed Morsi in 2013.
North Sinai has witnessed many violent attacks by militants since the January 2011 revolution that toppled president Hosni Mubarak.
The attacks targeting police and military increased after the ouster of Morsi. More than 600 security personnel have been reported killed since then.