A duty cycle detector includes a first ring oscillator suitable for including an odd number of first inverters and generating a first periodic signal by using the first inverters, at least one inverter among the first inverters being enabled during a time interval when a clock has a first value, a second ring oscillator including an odd number of second inverters and suitable for generating a second periodic signal using the second inverters, at least one inverter among the second inverters being enabled during a time interval when the clock has a second value. The duty cycle detector further includes a frequency comparator suitable for comparing a frequency of the first periodic signal with a frequency of the second periodic signal and generating a duty cycle detection signal of the clock.