Import Tool for tumblr from MT
It seems that there is no perfect way to import the past Movabletype entries to tumblr with a single click.
I have found some links which are either, a source code, or a web application which you need to fullfil your ID and PW for the tumblr.
I suppose since tumblr does not officially give you the import tools, the above solution is best you can get right now. I only found the source code made by Ruby, making it more confusing for me, so I might just change the password for the time being and let the some dude’s program do the work.