To provide an efficient sound deadening structure for reducing noise of a hydraulic breaker by directly reducing striking sound between a drive piston and a chisel without shutting out already generated noise.

A sound deadening structure for a hydraulic breaker is applied to a chisel that is a tool for crushing a crush target object that generates sound by being struck by a drive piston. In the sound deadening structure, the head of the chisel to be struck by the drive piston is coated with a noise reduction material.