An expansion valve having a solenoid relief valve equipped in an air conditioner for decompressing and expanding a refrigerant compressed by a compressor and supplying the same to an evaporator, the expansion valve comprising: a valve body which comprises a valve chamber into which a high-pressure refrigerant from the compressor enters; a first passage through which flows the refrigerant traveling from the valve chamber toward the evaporator; a second passage through which flows the refrigerant returning from the evaporator toward the compressor; a valve seat disposed between the valve chamber and the first passage; and a refrigerant chamber disposed in parallel to the valve seat and communicating the valve chamber and the first passage; a valve means capable of coming into contact with and separating from the valve seat for opening and closing the valve seat; a power element which is a driving mechanism for the valve means; and characterised by a solenoid relief valve disposed between the refrigerant chamber and the first passage, wherein the solenoid relief valve comprises: a relief valve body having a relief valve chamber communicating with the refrigerant chamber; a relief valve seat disposed between the refrigerant chamber and the first passage; a relief valve means disposed inside the relief valve chamber, capable of coming into contact with and separating from the relief valve seat for opening and closing the relief valve seat, and which maintains a state of coming into contact with the relief valve seat from pressure of the refrigerant inside the relief valve chamber; a pilot valve chamber formed to the valve body, and which communicates with the relief valve chamber; a pilot valve seat disposed between the pilot valve chamber and a passage opening to the atmosphere; a pilot valve means disposed inside the pilot valve chamber, capable of coming into contact with and separating from the pilot valve seat for opening and closing the pilot valve seat; a plunger coupled to the pilot valve means, which moves the pilot valve means in opening and closing directions; and a magnet coil for driving the plunger. a valve body which comprises a valve chamber into which a high-pressure refrigerant from the compressor enters; a first passage through which flows the refrigerant traveling from the valve chamber toward the evaporator; a second passage through which flows the refrigerant returning from the evaporator toward the compressor; a valve seat disposed between the valve chamber and the first passage; and a refrigerant chamber disposed in parallel to the valve seat and communicating the valve chamber and the first passage; a valve means capable of coming into contact with and separating from the valve seat for opening and closing the valve seat; a power element which is a driving mechanism for the valve means; and characterised by a solenoid relief valve disposed between the refrigerant chamber and the first passage, wherein the solenoid relief valve comprises: a relief valve body having a relief valve chamber communicating with the refrigerant chamber; a relief valve seat disposed between the refrigerant chamber and the first passage; a relief valve means disposed inside the relief valve chamber, capable of coming into contact with and separating from the relief valve seat for opening and closing the relief valve seat, and which maintains a state of coming into contact with the relief valve seat from pressure of the refrigerant inside the relief valve chamber; a pilot valve chamber formed to the valve body, and which communicates with the relief valve chamber; a pilot valve seat disposed between the pilot valve chamber and a passage opening to the atmosphere; a pilot valve means disposed inside the pilot valve chamber, capable of coming into contact with and separating from the pilot valve seat for opening and closing the pilot valve seat; a plunger coupled to the pilot valve means, which moves the pilot valve means in opening and closing directions; and a magnet coil for driving the plunger. a relief valve body having a relief valve chamber communicating with the refrigerant chamber; a relief valve seat disposed between the refrigerant chamber and the first passage; a relief valve means disposed inside the relief valve chamber, capable of coming into contact with and separating from the relief valve seat for opening and closing the relief valve seat, and which maintains a state of coming into contact with the relief valve seat from pressure of the refrigerant inside the relief valve chamber; a pilot valve chamber formed to the valve body, and which communicates with the relief valve chamber; a pilot valve seat disposed between the pilot valve chamber and a passage opening to the atmosphere; a pilot valve means disposed inside the pilot valve chamber, capable of coming into contact with and separating from the pilot valve seat for opening and closing the pilot valve seat; a plunger coupled to the pilot valve means, which moves the pilot valve means in opening and closing directions; and a magnet coil for driving the plunger.