A touch panel device according to the present invention includes: a stylus pen including a conductive stylus pen electrode portion at a tip portion thereof; a plurality of capacitance detecting interconnections formed on a substrate in row and column directions; an oscillator circuit which outputs an oscillation signal for performing charging/discharging to each of the plurality of capacitance detecting interconnections, the oscillation signal having a cycle which changes in accordance with an amount of electric charges in the charging/discharging; and a counter circuit and a computing circuit/control circuit which compute, based on a change of the cycle being in accordance with a capacitance formed between the electrode portion of the stylus pen and the capacitance detecting interconnections, positional coordinates of the stylus pen brought in proximity to the capacitance detecting interconnections in a non-contact manner, wherein the stylus pen outputs to the electrode portion of the stylus pen an input pen signal which is in synchronization with the oscillation signal, has a phase different from a phase of the oscillation signal, and has a larger voltage amplitude compared with the oscillation signal.