A liquid sending failure detector acquires periodically a liquid sending pressure of a liquid sending mechanism consecutively sends liquid using at least one plunger pump that sends liquid by reciprocally driving a plunger such that a fluctuation is read in one driving period of the liquid sending mechanism, and detect a liquid sending failure of the liquid sending mechanism using an acquired liquid sending pressure. The liquid sending failure detector executes a pulsation detection step of obtaining a fluctuation range of the liquid sending pressure in a certain driving period of the liquid sending mechanism and detecting pulsation on a condition that a count of consecutive periods in which the fluctuation range exceeds a predetermined reference value exceeds a predetermined reference count, and a liquid sending failure detection step of detecting a liquid sending failure of the liquid sending mechanism when the pulsation is detected in the pulsation detection step.