Friction body, writing instrument and writing instrument set

The present invention provides a friction body, writing instruments with the friction body and a writing tool kit by the friction body and a writing instrument constituted only grazed the friction body in a reversible thermochromic ink pattern formed or handwriting when small area portion, without a substantial increase in pressing force or grazed times, you can make it change color selectively and easily. Said friction member, which may be reversible thermal discoloration pattern using friction heat from the first color state to the second state, the contact area between the aforementioned friction body on a glass plate with 1000g load when pressed at 0.5 ~ 15mm