A modular plug attaching and detaching tool includes a first holder configured to accommodate a plurality of modular plugs in an aligned state and a second holder configured to press unlocking claws of the plurality of modular plugs when the second holder is attached to the first holder. The first holder includes an engagement groove extending in an inserting direction of the modular plug. The second holder includes an engagement part configured to engage with the engagement groove of the first holder by being moved in the inserting direction.