A strip-shaped filter in the shape of a circular arc is arranged at a port opening portion of an oil passage, the port opening portion being in maximum proximity to a spool hole portion or a valve element, to prevent a contaminant in the oil passage from reaching the spool hole portion or the valve element. A groove portion is arranged to extend in a circumferential direction in a wall surface of the upper body which defines the spool hole portion. The port opening portion is defined in the groove portion, and is connected to the oil passage. The filter is housed in the groove portion to close the port opening portion defined in the groove portion.