Provided is a valve timing adjustment device that suppresses slippage of an assist spring, prevents disengagement, and facilitates assembly of the assist spring. A valve timing adjustment device adjusts an opening timing and closing timing of an intake valve or an exhaust valve of an internal combustion engine. In the assist spring, the inner peripheral end portion is formed in a non-bent shape, the outermost periphery is in contact with the rib, a second winding is in contact with the inner peripheral end portion, and there is no contact between windings from the second winding to the outermost periphery.