Abstract: An angle adjustment mechanism for use in a circular saw including a shoe, a bracket mounted to the shoe, an operating member slidably mounted to the bracket and a cutting unit pivotally mounted between the shoe and the operating member. The angle adjustment mechanism includes a positioning member that has an abutting portion and is mounted to the cutting unit and a limiting member that is pivotally mounted to the bracket and has a stop member operable between a stopping position where the stop member protrudes from the guiding bracket and a releasing position where the stop member is located away from the positioning member. The abutting portion of the positioning member is abuttingly positioned at the stop member when the stop member is located at the stopping position, such that the cutting unit can be quickly positioned to the desired angle.