1. A mobile station apparatus comprising:a transmitter configured to transmit a physical uplink control channel; and
a transmission power controller configured to:
compute a first power headroom for a subframe by assuming a predefined physical uplink control channel format, in a first case that the transmitter is configured not to transmit the physical uplink control channel in the subframe,
compute the first power headroom for the subframe based on a physical uplink control channel format of a transmitted physical uplink control channel, in a second case that the transmitter is configured to transmit the physical uplink control channel in the subframe, and
compute a second power headroom for the subframe, the second power headroom being a difference between a maximum transmit power value and a calculated transmit power value of a physical uplink shared channel; wherein
the transmission power controller is configured to instruct the transmitter to transmit the first or second power headroom for a certain uplink component carrier in case that at least one uplink radio resource for initial transmission is assigned to the mobile station apparatus and a power headroom report has been triggered and the transmission power controller determines to transmit the first or second power headroom through the at least one uplink radio resource for initial transmission on the basis of a priority.