self-inking rubber stamp
A stamp with a built-in ink pad that automatically re-inks the die after each impression. Common in office and personal use.
I bought a new self-inking stamp, so stamping documents has become easier.
Compound of 浸透 (しんとう, 'permeation, soaking') and 印 (いん, 'stamp, seal'), referring to the ink permeating through the stamp.