Abstract: A gas pressure detection device 10 detects a decrease in a pressure of gas of a gas balancer 8 of a robot 2. The gas pressure detection device 10 includes a calculating part configured to calculate a parameter Rt(?) indicating a magnitude relation between a reference pressure Pa(?) at a rotational angle ? of a rotary arm 14 and a measured pressure Pt(?) measured at the rotational angle ?, calculate a plurality of parameters Rt(?) based on a plurality of measured pressures Pt(?) at different measurement times, and calculate a moving average Rtj(?) of the parameter Rt(?) at a measurement time tj that is a j-th measurement time of the measured pressure Pt(?) (j representing a natural number of 2 or above), and a determining part configured to compare the moving average Rtj(?) with a reference value R to detect the decrease in the pressure of the gas.