The blast at the entrance to the town of Khales also wounded 37, according to Diyala province police spokesman Colonel Ghalib al-Attiyah and health department spokesman Faris al-Azzawi.
Attiyah said the checkpoint was crowded with cars, and that a number of them were burned in the blast.
There was no immediate claim of responsibility for the attack, but the Islamic State jihadist group carries out frequent suicide bombings in Iraq.
The blast came a day after a suicide bombing claimed by IS killed at least 15 people in Baghdad's Kadhimiyah neighbourhood.
IS overran large areas north and west of Baghdad in 2014, but Iraqi forces have since regained significant ground and are conducting operations to set the stage for the battle to recapture Mosul, the last IS-held city in the country.
The jihadists have responded to the battlefield setbacks by striking civilians, and experts have warned there may be more such attacks as the jihadists continue to lose ground.