To provide a device and a method for trimming a tire in which a spew can be cut off precisely.

The device for trimming a tire includes an image pickup device 3 which can pick up a tire including at least the profile of a tread portion thereof approximately from the side of the tread surface, an image data storage means 4 which can store an image data of the tire picked up by the device 3, an image processing device 7 which can identify a spew 5 of the tire using the image data to set a blade edge target line of a spew cutter 6 along the root of the spew 5, and a spew cutting means 9 which sets the cutter 6 on the blade edge target line of a rotating tire 2 to cut off the spew.