Disclosed herein is a portable putting practice device, which is constructed so that a mat 30 is wound up in a roll to be stored in a box 20, and is unwound and pulled out of the box for use. The device includes foldable flexible guide walls which are provided on both side ends of the mat in a longitudinal direction thereof and prevent a golf ball from escaping from the mat when it is in use. When a user desires to store the mat in the box, the guide walls 40, 50 are unfolded outwards relative to left and right ends of the mat such that they are on the same plane as the mat. In this a state, the guide walls are wound. Meanwhile, when the user desires to use the mat 30, the mat is unwound and pulled out of the box 20.