A mobile telecommunication terminal device is provided which is capable of preventing an excessive increase in transmitting power to be fed from a base station even if a burst error occurs in a mobile unit. The mobile telecommunication terminal device has an error frequency calculating section to calculate a frequency of detection of errors in received data, a target transmitting power setting section to decrease a set value of a target SIR (Signal to Interference Power Ratio) when the frequency of detection of errors is not larger than the target SIR, while the frequency of detection of errors exceeds the target detection frequency value, to increase the set value of the target SIR, an SIR measuring section, an SIR comparing section, a transmitting power requesting section, and an error frequency correcting section.