To significantly reduce the bearing on top of a boss hole of a pin boss part in the connection structure of a piston and a connecting rod of an internal combustion engine.

The connection structure comprises the piston, a piston pin, the connecting rod and a connecting means. The piston has the pin boss part formed on the rear side of a piston body and a gap formed on the opposite side of the pin boss part from the piston body. The piston pin inserted into the boss hole formed on the pin boss part has a notch groove between the gaps formed on the pin boss part. The connecting rod has a connecting part on one end side of a rod body to be engaged with the notch groove of the piston pin. The connecting means is for connecting the connecting part to the piston pin.