Hello DY HAN
According to the routing table entry of “S” this is a statically configured default route. This means that there is a command in the config in the form of
ip route 0.0.0.0 0.0.0.0 1.1.1.1
SInce the “S” is indicated at the beginning of the route, it means that no dynamic routing protocol is involved, nor is HSRP. It is manually configured on the device. as shown above.
Now the “*” indicates that it is a candidate default route. This just indicates that, if there is more than one default route, this one, in particular, is the currently used one. It looks like there is only one configured on your device, so by definition, this is the one being used.
I hope this has been helpful!
Laz