A power transmission device of a non-contact power transmission system includes a waveform monitoring circuit that generates and outputs a waveform-monitoring induced voltage signal based on a coil end signal of a primary coil, and a power transmission control device that controls a power transmission driver that drives the primary coil, the power transmission control device receiving the waveform-monitoring induced voltage signal and detecting a change in waveform of the induced voltage signal to detect a power-reception-side load state. The waveform monitoring circuit includes a first rectifier circuit having a limiter function, the first rectifier circuit including a current-limiting resistor provided between a coil end node where the coil end signal of the primary coil is generated and a monitoring node where the waveform-monitoring induced voltage signal is generated, performing a limiter operation that clamps the induced voltage signal at a high-potential-side power supply voltage, and subjecting the induced voltage signal to half-wave rectification.