Hydraulic fracturing stress measurement technique is the most well-known method for in situ stress measurements. However, a general method has not yet been established for estimating the reliability of the evaluated in situ stress. This paper presents a new method for estimating the reliability of the in situ stress evaluated by hydraulic fracturing stress measurement technique which utilizes a shut-in pressure and an orientation of cracks induced by hydraulic fracturing. The validity of the method was examined by applying it to two sets of artificial data constructed for eight cracks under a given stress state. The shut-in pressure for each crack was given by assuming the shut-in pressure to be equal to the normal stress acting perpendicularly to the crack. It was revealed that the shut-in pressure for each crack was most crucial for obtaining reliable results.