A target detection device is provided, which includes a transmission array and a signal generator. The transmission array includes a plurality of transmission elements configured to convert an electric signal into a transmission wave. The signal generator generates first and second sets of electric signals, each set being generated with different phase settings. The signal generator groups the transmission elements according to grouping configurations including first and second grouping configurations. In the first grouping configuration, the plurality of transmission elements are grouped into a plurality of groups each having p transmission elements, and, in the second grouping configuration, the plurality of transmission elements are grouped into a plurality of groups each having q transmission elements. The signal generator inputs the first set of electric signals to each group of the first grouping configuration, and inputs the second set of electric signals to each group of the second grouping configuration.