Abstract: A pressure detector for detecting a high side pressure from a high pressure side impulse line and a low side pressure from a low pressure side impulse line includes a high side pressure variance calculating section for calculating a high side pressure variance from a high side pressure fluctuation calculated from a high side pressure signal, a low side pressure variance calculating section for calculating a low side pressure variance from a low side pressure fluctuation calculated from a low side pressure signal, a rate calculating section for calculating a variable according to a ratio of the high side pressure variance to the low side pressure variance, and a determining section for determining blockage of the high pressure side impulse line or blockage of the low pressure side impulse line based on a value of the variable.