Colin Farmer, 61, was stunned by police following reports of a man walking through Chorley with a samurai sword.
Farmer was walking to a pub to meet friends on Friday when a police officer fired the Taser. It forced him to drop his stick and he fell to the ground, BBC reported.
Farmer was taken to hospital for treatment and later discharged. "It felt like I was grabbing an electricity pylon," he said.
Farmer, who has suffered two strokes, said the experience had left him "shaking like a leaf" and scared to go outside.
Farmer said initially he thought he was being attacked by thugs.
A top official of Lancashire Police said the force had "deep regrets" and had "clearly put this man through a traumatic experience".
The case has been referred to the Independent Police Complaints Commission.