To provide a Boston bag allowikng height, length, or width to be changed whenever necessary and is economically used for a variety of purposes.

The Boston bag 1 includes: a bag body 2; bag body opening/closing means 3 provided along the length direction at an upper part of the bag body 2; a grip part 4 provided in such a way to protrude above the bag body 2; and joint means 5, 6, 7, and 8 provided in four corners of the bag body 2 respectively. In the joint means (5 and 6 or 7 and 8) provided on both sides in the length direction respectively, one side has male latches, whereas the other side has female latch; in the joint means (5 and 7 or 6 and 8) provided horizontally on both sides respectively, one side has male latches, whereas the other side has female latch. By joining the joint means 5, 6, 7, and 8 each other, height, length, or width is altered suitably and the bag is used for a variety of purposes.