Fourteen people were injured in the blast when a vehicle belonging to the Anti-Terrorism Force (ATF) accompanying Justice Zahoor Shahwani's vehicle was hit at Quetta's Zarghon road.
Balochistan Home minister Sarfaraz Bugti said the judge escaped the attack but one of the security vehicles escorting him was damaged.
The bomb was planted along the side of the road and exploded as the Anti-Terrorism Force (ATF) vehicle passed by.
Police spokesman Shahzada Farhat said police officers and passers-by were wounded.
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Security forces and a bomb disposal squad reached the scene to collect evidence. Rescue teams moved the injured to nearby hospitals.
Police cordoned off the area as a search operation went underway.
"This is a busy road and the terrorists take advantage of this, planting bombs and fleeing on motorcycles," Bugti said, strongly condemning the attack.
"We are reviewing our security measures and you will see changes on the ground," he said.
Bugti said that three to four kilogrammes of explosive material was used in the blast.
The explosion comes just days after a suicide bombing killed 74 people and injured 115, mostly lawyers and journalists, at the emergency ward of Quetta's Civil Hospital on Monday.
A combing operation is ongoing throughout Quetta following Monday's blast.