Memory device and operating method of the memory device

A method of operating a memory device, the method comprising:

• performing a program voltage apply operation of programming selected memory cells among a plurality of memory cells;
• determining a length of a floating period in which a common source line is floated, based on a count value of a program loop in which the program voltage apply operation is included;
• and
• applying a common source line voltage to the common source line while the program voltage apply operation is performed, and then floating the common source line during the floating period.

A memory device comprising:

• a plurality of memory cells connected between a common source line and bit lines;
• a peripheral circuit configured to perform a program operation including a plurality of program loops, in which data is stored in selected memory cells among the plurality of memory cells;
• and
• a program operation controller configured to control the peripheral circuit to apply a common source line voltage to the common source line in a program voltage apply operation included in any one program loop among the plurality of program loops and then float the common source line during a floating period,
• wherein a length of the floating period is determined based on a count value of the one program loop.