Cutting insert and cutting tool on which same is mounted

A cutting insert for right angle machining, comprising

• two opposing side surfaces, four rectangular upper surfaces extending between the two side surfaces, a fastening hole penetrating the two side surfaces, and cutting edge portions formed at positions where the side surfaces and the upper surfaces are connected to each other, wherein the cutting insert is 180° rotationally symmetric about a virtual center line passing through a center of the fastening hole, and 180° rotationally symmetric about a virtual center line passing through a center of the upper surfaces,
• the cutting edge portions comprise
• a second main cutting edge formed on long sides of the upper surfaces, a first main cutting edge connected to the second main cutting edge at an angle, a corner cutting edge connected to the first main cutting edge, and a sub cutting edge formed on short sides of the upper surfaces and connected to the corner cutting edge,
• the side surfaces comprise
• a side flat surface surrounding the fastening hole, a second main cutting edge clearance surface extending from the side flat surface and connected to the second main cutting edge, and a first main cutting edge clearance surface extending from the side flat surface and connected to the first main cutting edge, and connected to the second main cutting edge clearance surface at an angle, and
• when viewed from the upper surfaces,
• an angle formed by an extension line of the first main cutting edge and an extension line of the side flat surface is greater than or equal to an angle formed by an extension line of a boundary line of the first main cutting edge clearance surface and an extension line of the side flat surface.