A data acquisition device comprising: an integrated circuit having a first terminal to which a master/slave switching signal is input at a start of data acquisition, an A/D converter for converting analog input data to digital data, and an output terminal for outputting the digital data, the integrated circuit operating in either a master mode or a slave mode according to the master/slave switching signal; and an information processor having a switching setting part configured to generate the master/slave switching signal, a second terminal connected to the first terminal and for output the master/slave switching signal, and an input terminal connected to the output terminal and for receiving the digital data, the switching setting part configuring the information processor to operate in the master mode when the integrated circuit operates in the slave mode, and to operate in the slave mode when the integrated circuit operates in the master mode, wherein the integrated circuit is configured to output a synchronizing signal to the information processor to allow the information processor to acquire the digital data and configured to output the digital data from the output terminal, when operating in the master mode according to the master/slave switching signal supplied from the information processor, wherein the information processor is configured to generate a system clock and correct a timing of the system clock using the synchronizing signal supplied from the integrated circuit when the information processor is in slave mode, characterized in that the information processor is configured to reduce a clock frequency, when the information processor is configured to operate in the slave mode, compared with a state where the information processor is set to the master. an integrated circuit having a first terminal to which a master/slave switching signal is input at a start of data acquisition, an A/D converter for converting analog input data to digital data, and an output terminal for outputting the digital data, the integrated circuit operating in either a master mode or a slave mode according to the master/slave switching signal; and an information processor having a switching setting part configured to generate the master/slave switching signal, a second terminal connected to the first terminal and for output the master/slave switching signal, and an input terminal connected to the output terminal and for receiving the digital data, the switching setting part configuring the information processor to operate in the master mode when the integrated circuit operates in the slave mode, and to operate in the slave mode when the integrated circuit operates in the master mode, wherein the integrated circuit is configured to output a synchronizing signal to the information processor to allow the information processor to acquire the digital data and configured to output the digital data from the output terminal, when operating in the master mode according to the master/slave switching signal supplied from the information processor, wherein the information processor is configured to generate a system clock and correct a timing of the system clock using the synchronizing signal supplied from the integrated circuit when the information processor is in slave mode, characterized in that the information processor is configured to reduce a clock frequency, when the information processor is configured to operate in the slave mode, compared with a state where the information processor is set to the master.