An apparatus and a method for detecting imbalances between an I-channel signal and a Q-channel signal in order to suppress a spurious signal in a direct conversion digital quadrature transmission system is disclosed. The apparatus includes: a compensation signal generating unit for generating a first and a second compensation signals based on a digital I-channel and a digital Q-channel signals; a baseband signal generating unit for generating an I-channel and a Q-channel baseband signals by converting a radio frequency signal into a low frequency signal; and a detecting unit for detecting a phase imbalance and an amplitude imbalance between the digital I-channel and the digital Q-channel signals by using a correlation between the first and the second compensation signals with the I-channel and the Q-channel baseband signals.