In a communication system in which a mobile station apparatus is connected to a base station apparatus simultaneously using a plurality of frequency bands, an event is efficiently determined concerning measurement of reception qualities of the frequency bands. The mobile station apparatus includes: a reception unit that receives from the base station apparatus an event condition for measuring a reception quality of at least one carrier component defined in the frequency bands different from each other and a parameter used for determining whether or not the event condition is satisfied; a measurement processing unit that measures the reception quality of the at least one carrier component; a cell determination unit that determines whether to adjust the received parameter; and an event determination unit that sets the event condition based on the received parameter or the adjusted parameter and that determines whether or not the set event condition is satisfied.