A solenoid valve comprising: a main valve having a valve seat provided in a main flow passage, and a main valve body seated on or unseated from the valve seat to open or close the main flow passage; a pilot passage that branches from the main flow passage; an orifice provided in the pilot passage; a back-pressure chamber connected to the pilot passage downstream from the orifice, the back-pressure chamber being configured to bias the main valve body to a closing direction by virtue of an internal pressure; a pilot valve disposed in the pilot passage downstream from a connection point to the back-pressure chamber, the pilot valve being configured to control an internal pressure of the back-pressure chamber; and a solenoid (Sol) configured to control a valve opening pressure of the pilot valve, wherein when the pilot valve is opened from the closed state, the internal pressure of the back-pressure chamber rises over the valve opening pressure of the pilot valve only for an instant, then, as the pilot valve is opened, and the pressure of the upstream side of the pilot passage is released, the pressure of the back-pressure chamber decreases to the valve opening pressure, wherein there is a time difference between a valve opening timing of the main valve and a valve opening timing of the pilot valve such that the valve opening timing of the main valve is delayed from the valve opening timing of the pilot valve, the main valve is not open by the pressure in the main flow passage when the pilot valve reaches the valve opening pressure, a valve opening pressure of the main valve is set so as to be a pressure exceeding the pressure in the main flow passage required to open the pilot valve, and characterized in that the time difference between the valve opening timing of the main valve and the valve opening timing of the pilot valve is set by a ratio between a front face-side pressure receiving area (As) where the main valve body receives a pressure of upstream of the main flow passage and a rear face-side pressure receiving area (Ah) where the main valve body receives the internal pressure of the back-pressure chamber. a main valve having a valve seat provided in a main flow passage, and a main valve body seated on or unseated from the valve seat to open or close the main flow passage; a pilot passage that branches from the main flow passage; an orifice provided in the pilot passage; a back-pressure chamber connected to the pilot passage downstream from the orifice, the back-pressure chamber being configured to bias the main valve body to a closing direction by virtue of an internal pressure; a pilot valve disposed in the pilot passage downstream from a connection point to the back-pressure chamber, the pilot valve being configured to control an internal pressure of the back-pressure chamber; and a solenoid (Sol) configured to control a valve opening pressure of the pilot valve, wherein when the pilot valve is opened from the closed state, the internal pressure of the back-pressure chamber rises over the valve opening pressure of the pilot valve only for an instant, then, as the pilot valve is opened, and the pressure of the upstream side of the pilot passage is released, the pressure of the back-pressure chamber decreases to the valve opening pressure, wherein there is a time difference between a valve opening timing of the main valve and a valve opening timing of the pilot valve such that the valve opening timing of the main valve is delayed from the valve opening timing of the pilot valve, the main valve is not open by the pressure in the main flow passage when the pilot valve reaches the valve opening pressure, a valve opening pressure of the main valve is set so as to be a pressure exceeding the pressure in the main flow passage required to open the pilot valve, and characterized in that the time difference between the valve opening timing of the main valve and the valve opening timing of the pilot valve is set by a ratio between a front face-side pressure receiving area (As) where the main valve body receives a pressure of upstream of the main flow passage and a rear face-side pressure receiving area (Ah) where the main valve body receives the internal pressure of the back-pressure chamber.