To make it possible to determine an accurate soil quality by collecting detailed test data.

A sprocket, which is turnable along a guide chain of a post 2, is provided on a carrier 3. A sensor is provided so as to detect the rotary speed of the sprocket while the penetration speed of a penetration rod 7 is computed based on the detected value of this sensor and this penetration speed is compared with a preliminarily determined reference penetration speed. Responding to the result, each penetration condition for the load, drive of a rotary drive source or the like is changed while the test data is recorded every time when the penetration conditions of the penetration rod 7 are changed. This construction makes it possible to record detailed test data in the penetration test whenever the penetration condition is changed and moreover, to eliminate such disadvantages that the test data may vary with an inspector in charge.